The Legend of Korra/WMG/The Gaang's Descendants

For theories about other subjects, see The Legend Of Korra Wild Mass Guessing Index.

Toph's Baby Daddy/Boyfriend/Husband
Teo? The Duke? Haru? Sokka? Random guy with whom she had a fling?
 * Probably Ohev, a book-only character who used to work at the Beifong estate and fell in love with Toph.
 * No no. It was totally just some random tax accountant she first met in her twenties and they fell for each other, mystifying their friends. Toph married a Muggle.
 * Alternately: There isn't one, she's adopted.
 * Unlikely. Lin looks very much like her grandmother Poppy, and she also has the same minty green eyes as Toph (albeit without blinding cataracts).
 * That has nothing, at all, to do with anything in this post. And no, she's not adopted.
 * Of course she's not. She's the picture of Poppy Beifong, Toph's mother.

Lin Beifong got her scars from early attempts at adapting metal cables as a weapon
It's confirmed she developed the technology. If you know just what kind of damage a metal cable under tension is capable of, it's not surprising what a momentary lack of control could cause.

Toph never married; Lin was born out of wedlock
It's entirely fitting for the character, really. Out of all the Gaang, Toph would be my bet for "least likely to get married" (and not just because she's one of the few characters not explicitly paired up by the end), but I imagine she'd also be pretty open to one-night stands or short relationships. It also explains why Lin took her mother's last name. Alternate Theory: Toph reproduced by parthenogenesis
 * Parthenogenesis would require Lin to have Toph's exact genome, which doesn't seem likely seeing how different their hairs are.

Chief Lin Beifong did not get along with Toph.
I could see it happening - a strained relationship between the parent and child... Beifong family tradition, perhaps? Lin's attitude just seems in so many ways different from Toph's... Although they do have certain similarities. I feel like they've had their fair share of disagreements as mother and daughter though. Maybe, at one point in the series, Lin will stare up at that giant statue of her mother located at police HQ.. And some kind of scene will occur. Perhaps involving Tenzin.
 * It may have stemmed from Toph's relationship with her father. Her mother was happy to see her home and safe, but her father's still upset at Toph for running away and blamed the Gaang for encouraging her. And he STILL won't admit that Toph can take care of herself and attempted to have her confined in their home with more guards watching her every move. This makes her even more rebellious and would escape her house a couple times before being returned. When Toph's daughter Lin is born, he raised her to follow tradition which he failed with Toph. That includes raising Lin to hate the Avatar and other benders.

Chief Lin Beifong is actually Toph's adopted daughter
This troper can't really picture Toph settling down with anyone for long enough to have a daughter. Plus, it could help make a point about non-bender oppression: Toph could have specifically sought out a baby who showed strong earthbending potential, so she could raise another metalbender. It seems like something that could become a common trend - if you bend an element, wouldn't you want a kid with potential to bend the same thing?
 * Even though this is a kid's show, thus one-night-stands are usually frowned upon as a method of producing children, I'd have to point out that it's kinda silly to say that in the 20-30 years between ATLA's end and when Lin would have been born, it would be impossible for Toph to marry someone. Most of the most badass people in history still had families at home.

Lin Beifong's FATHER died during childbirth
It makes it a moot point as to who he was. It says enough on its own
 * I didn't know fathers could give birth, let alone die from it.

Lin's "Father" is Azula!

 * Con...firmed?

Lin arrested Aang at least once while he was still alive.
Avatars don't seem to impress her much. And besides, breaking all those cabbage carts had to catch up with Aang at some point.
 * Unlikely. Aang founded the Republic.
 * I support this. More than once Aang has let himself be arrested to prove he respects justice. I could see him doing property damage and going to court like any other citizen to pay his fines.
 * Unlikely. According to Tenzin, Lin and Aang got along really well.

Wei Beifong is Chief Beifong's daughter and a non-bender.
Aang and Katara have grandchildren in LoK, why couldn't Toph? And as for the non-bender part, consider this theory. Imagine you're the heir to a famous line of powerful earthbenders, your grandmother was a war hero and your mother is a decorated police officer, only you can't bend. Lots of angsty possibilities there, especially if she fell in with a bad crowd. And it be something of a deconstruction of the fanbase's idolization of Toph, by showing what it's like to live in the shadow of such badassness.

Lin Beifong doesn't like Korra because she blames the Avatar for her mother's death

 * We know there was some unpleasantness involving someone named Yukon. Maybe Toph died and Lin believes Aang could have saved her.
 * Possibly jossed. According to Tenzin, Lin has issues with Korra because he used to be in a relationship with Lin and things went sour.

We will meet Firelord Zutara
Zuko and Mai wanted to name their daughter after the woman who saved Zuko's life and kicked Azula's ass, but, since 'Katara' was too Water Tribe-y for the heir to the throne, they gave the name a Fire Nation twist. Incidentally, this now means Kataang, Maiko, and Zutara are all canon.
 * This...is too awesome to happen. Sadly.

Zuko's Great-grandson will be the Blue Spirit
He will be a sort of robin hood figure and Korra will meet him while he's stealing from her. He's either been disowned or sent by his Grandfather on a journey like he was. May or may not be a fire bender.
 * Alternatively, KORRA will be the new Blue Spirit.

There will be a circus troupe ran by Ty Lee's daughter.
Because of course.

We will meet either Teo or one of his descendants...
And he will be a knock-off of Dr. Weird. Why? ...Why not?
 * Teo: Gentlemen (Beat) and female Avatar, BEHOLD!
 * Teo's descendants will build the world's first air plane. Somehow, Korra will end up hijacking it to save the day... and crash it into a cabbage stand.

At least one of the Gaang's descendants is on the United Republic Council alongside Tenzin.
Sokka, being the next Water Chief, probably has a son on the council. What I am wondering the most about is who is representing the Northern Water Tribe. Yue was an only child. Who did the icy crown succeed to?

Aang's elder children, Kya and Bumi, are Equalists
Of Aang's three children, only Tenzin was an airbender. Therefor Aang might have favored him more and caused the other two to become jealous and hate all bending.
 * Possibly Jossed. Aang and Katara's oldest daughter, Kya, is a waterbender. Bumi, the middle child, is the only non-bender however.

One of Aang's non-bending children will turn out to be Amon.
So far, we only know that of Aang's children, Tenzin is the airbender. What better cause for a slow build of rage and resentment towards benders than a child of the Avatar who saved the world, who is ignored by the world JUST because he doesn't have the same magical powers as his parents and younger brother? It would be another very interesting angle on Aang's family and would make for a fun dynamic between Amon and Tenzin.
 * Not to mention Amon and Korra.
 * Aang and Katara's oldest daughter, Kya, has been confirmed to be a waterbender. This leaves Bumi as the only non-bender of the family...
 * Supported by the fact that Amon is a Energybender. Perhaps Bumi inherited the most powerful skill of all.
 * Might be jossed, Bumi has dark skin, whereas Amon has light skin, judging by what we see of his hands.

Aang's son Bumi will be introduced as a slimpy antagonist.
Look at the guy. He looks pretty shifty and untrustworthy. He'll probably appear like an Equalist sympathizer who doesn't get along with his siblings, and Korra will catch him doing some shady deals with them, but no-one will believe her. In the end she'll confront him personally...and find out that he belongs to Chief Beifong's secret police and has been trying to catch Amon for months when she blows his cover. Seriously, remember who this guy is named after, and what first impression he gave??
 * That scenario is now too similar to what 'The Aftermath'  But no arguments against the idea of Bumi being as...eccentric and initially off-putting as his namesake.

Amon is Lin's father.
With all the wild speculation as to each of their identities...it would be bizarrely appropriate.

Bumi ISN'T Amon but the team believes he is.

 * He would admit that he was jealous that his siblings can bend but he can't at first and/or feared of being rejected by his parents. But a revealed that his family accepted and still loved him the way he is. It can be an Expy for a child who's coming out of the closet.

Lin Bei Fong's scars
Lin got them from the same insident that killed Toph.

Lin Beifong will frequently suffer The Worf Effect several more times in the future
She, so it seems she is being built up to this in the series. Given it is only seven episodes in, she will likely get defeated or outsmarted several more times in the future of the series.

Kya lives in the South Pole.
She is a waterbender, and it's only logical for her to live there so that her mother wouldn't be alone in her old age.

Either Bumi or Kya have an airbender child.
Hey, they both have the potential. When the child gets older, s/he will be sent to live with Tenzin for a while so they could master their airbending abilities.

Lin will teach Bolin classical earthbending and metalbending
She certainly has the time to do so now that she resigned and Bolin's earthbending could do some work so who better than learn it from the one who was taught by the best?
 * Adding to that, it'll be part of his Character Development into maturity where the mindset of sensing and bending the impurities reflects him being more Let's Get Dangerous like his match against the Boarcupines only applied to real life.

Kya lives in the North Pole training a CIA/Navy SEAL (pun not intended) Amazon Brigade
To show progress from the NP's old mindset, Kya trains the women from merely healers to Combat Medics, namely in Bloodbending to do the "less-popular" jobs (yeah, yeah "wet work") that initially are thought of only as a myth/joke by the ladies being ridiculously girly only to don camo at night and "get results." Kya will only be really involved when the Equalists become seen as global threats about to spill out into the rest of the world where is guarding the coast as an admiral waiting for the signal from the Krew.

Bumi is not an antagonist, but merely a Brilliant but Lazy party boy
Instead of all the theories of him being Amon/An Equalist where he has "Bender Envy" ("I'm the son of the Avatar/greatest heroes of our generation and my siblings are powerful benders!") he's thinks not being a bender frees him of responsibilities ("I'm not a bender? PARTY TIME!) like being a Jackson not named Janet or Michael or a Kennedy not involved in politics, but liking the name recognition anyway. He's intro'd with a lot of women on his big arms, calling Tenzin "Tenz/Tenzy," Bei Fong "Rock Queen," etc., and basically being Big Fun that Bolin is/wants to be when he's that age with a talent for machines instead like Uncle Sokka, but a Cowardly Lion/ Lazy Bum that wants to avoid conflict as much as possible. Asami calls him out on that as a fellow non-bender that he's just as valuable/responsible as her in fighting the Equalists, proving it against them like Katara inspired the earthbenders to rebel on that ship. He pulls a Big Damn Heroes to assist and becomes her sensei like Piandao to Sokka, provides vehicles to anti-Equalist non-benders and especially a (marketable) tricked-out Cool Car and/or motorcycle for Asami to replace the read roadster Korra got that's more combat-orient for epic vehicle battles.
 * I just pictured Kamina, but with the laziness. He likely looked up to Sokka and the Kyoshi warriors, likely learning numerous things to craft himself into a unique person. Given the spirituality of the family, he likely knows Energybending and ways to reverse it.
 * Honestly, I don't think he needs to know it and be more of a fun cross between Uncle Sokka in effectiveness and namesake!Bumi in non-linear thinking. The key here is that he doesn't need to be the cure/mentor on Energybending like what's been floated around before and effectively be a good counterpart to  like he long could've been their world's equivalent of Edison/Da Vinci/Steve Jobs decades ago, but was more focused on partying and picking up chicks. Additionally, This Troper pictures Kevin Michael Richardson (again) as his voice, but with a different tone like The Boogeyman.

Bumi is a multi-skilled Badass Normal and currently owns Sokka's Space Sword
Doubling as a Call Back, Bumi likely learned a variety of skills to make up for a lack of bending, and probably spent the time traversing the world to learn, discovering the Sword covered in vines and plants. To add more, he learned the normal Water Tribe skills of tracking, weapons, and sarcasm. If he spent time with Sokka especially, he likely learned chi-blocking from the Kyoshi warriors. Since he was named after the Trickster Mentor himself, he likely took the time to be the type who would think outside the box and resort to using wits and creativity. In general, he's a Memetic Badass waiting to appear in Republic City.
 * For added emphasis, Tenzin will feel worried when he hears of him showing up, given he and Kya were the wild ones.
 * Bumi is a ninja! Crazy Uncles Sokka and Zuko taught him a few things. Zuko taught him "sneak", Sokka taught him "ATTACK!" SNEAK ATTACK SLICE!!

Lin will die
Does no one else feel that she's being set up for this?

The thing that put strain on Tenzin and Lin's relationship was
He wanted children. She didn't. Tenzin, as the last airbender would have felt a responsibility to have children and keep airbending alive. But Lin wasn't sure she wanted to start a family. This gradually put a strain, and a wedge in their relationship.

Lin's father will never be revealed
Bryke are magnificent trolls, and therefore they shall either wait until the series is almost over or leave the fandom clueless forever.

Sokka taught Bumi how to use a boomerang
He also taught him that you don't have to be a bender to be a badass. In the event that Sokka didn't have any kids of his own (or his kids simply weren't interested), he left his boomerang to Bumi when he passed away.

Zuko's daughter's name is
Zutara.

The next Earthbending Avatar...
Will be Lin's great-great-grandson, and be a Handsome Lech who tries to slack off from his duties as Avatar. He'll be accompanied by a young Firebending man with a hot-headed personality and a young Waterbending girl with an icy personality. His Airbending teacher will be Meelo, who's become quite the Cool Old Guy.

Lin's scars came from her mother.
Toph is a firm believer in the school of hard knocks, and wouldn't hold back even in a sparring match. Especially if Lin was a recruit to the Metalbending Police, and she had to show both her and other recruits that her daughter would get no special treatment from her. Those twin scars definately look like they came from a metalbender's double whip.