Yu-Gi-Oh! Zexal/WMG

Number C39: Utopia Ray has the potential to be the strongest monster in the game.
The highest predetermined ATK for a monster is 5000, Utopia Ray has an effect that causes an opponent's monster to lose 1000 points while itself gains 500 for each Overlay Unit it uses, Utopia Ray usually has 3, forcing the 5000 points to 2000 while the former gains 1500 points to its own 2500 attack points, making it a one turn 4000-ATK beatstick with at least twice the strength of the weakened monster.

Shark's motorcycle is (or was) a duel runner.
I mean look at it, it looks a lot like Antinomy's duel runner.

Astral is evil.
Think about it. If Astral is benign, why are all the Numbers cards acting the way they are? Because their original holder is evil and they still hold the feelings from his memories! Given what Dr Faker's doing, a case can be argued that he's a Well-Intentioned Extremist and is just trying to protect his world at the expense of Astral's. Astral losing his memories is probably part of a Memory Gambit, or just an accident.
 * Relatively confirmed, if No. 96 Black Mist is to be believed, as of Episode 37. It was directly stated that Astral was to destroy the world.
 * Astral will do a Face Heel Turn when he gets his memories back.
 * Astral maps out to the Split Personality archetype (kinda). Consider the other split personalities that Yu-Gi-Oh heroes have had. Yeah.
 * Astral will suffer major Amnesiac Dissonance when he gets them back. Fortunately, like the Pharaoh, hanging around Yuma is good for him so he will not go back to how he was.
 * Confirmed, sort of. Provided Black Mist is telling the truth.

Astral is Yusei from another universe.
WARNING: There are unmarked spoilers for 5D's ahead.

In another universe, the events of 5D's have progressed as in canon. However, when working one day, an accident happens and Yusei is sucked into the Momentum reactor. Years later, the Machine Emperor invasion and Momentum explosion still occur. During the Zero Reverse, Yusei's soul was thrown in between dimensions. Yuma accidentally used the Emperor's Key to open a dimensional rift, and Yusei - somehow thinking his name was Astral - fell through.

As Astral, Yusei retains his tendencies as The Stoic and as a genius duelist. One of the reasons why he sticks by Yuma is because of his Anime Hair, which vaguely resembles Yusei's own. He also reminds Yusei of Rally, a kid he took care of and viewed as a younger brother.

The only reason the Astral World looks different is because Astral does not have all his memories; once he does, it will reach a more definite appearance. The trash Dr. Faker is dumping is only contributing to the ruin of the world; the screams Haruto hears are from the despairing souls drifing around the world and within Momentum.

His memories were turned into the Numbers - who are destructive because they were corrupted by the Zero Reverse. Each Number, in addition to being based on the desires of people, are also vaguely based on Yusei's own memories (No. 34 Tera-Byte is based on Bruno, while No. 17 Leviath Dragon has a similar roar to Stardust). The one Number he held on to - No. 39 Aspiring Emperor Hope - is based on that vague idea of hope Yusei talked about while battling Aporia.


 * In episode 20, Astral flashbacks to . Momentum out of control?

There will be a Zexal expy for Red-Eyes Black Dragon.
We already got Galaxy Eyes, its only a matter of time for its counterpart to appear and become Shark' or Fuuya's monster. And on that matter, it'll probably be named something like Solar-Eyes Electron Dragon, just to keep with the "opposites" thing it inherited with Red-Eyes.
 * I'm throwing out something like Darkhole Dragon

Kaito is Paradox without Zero Reverse ruining his life.
Since Yusei and co. prevented the Second Zero Reverse, Kaito didn't become Paradox.

Zexal takes place before 5Ds.
Think about it: In the "legendary Duel Monsters" episode, only DM and GX monsters were shown. Fusion and Special Summon monsters have been used, but no Synchros have been shown. Even the lack of D-Gazers in 5Ds can be explained- the constantly-moving scenery and rapid eye movements of the players would be too erratic to properly display AR, so DM-style holograms are used instead.

The numbers are originally from...
The Other Side. .

Akari and Aki are somehow related.
Akari and Aki really look too similar to not be related in some way. Depending on whether you place Zexal before or after 5Ds, Akari could be Aki's grandmother, grandchild, ect. If she changed her name, Akari could even be Aki's mom...

Zexal takes place 200 years after the original series.
Explains all the new technology, and why no one remembers the legendary dragons.

Yuma will die.
Yuma will die, and someone will become the new host for Astral.
 * It's doubtful that Yuma will die, per se. The way these anime contracts tend to work is that the contract will threaten somebody close to Yuma (i.e. Kotori) or the relationship between the two of them. Probably the former, given this is a Shonen anime.

Yuma will die, its stated in his contract. Probably tragically, might ask Kaito/Shark/someone to kill him or something. Timeskip happens (short or long, who knows) and members of Yuma's group will take turns taking care of Astral. Astral will duel alongside both Shark and Kaito, each offering them super modes. Then Yuma comes back, EVIL.
 * Suddenly the show got a lot more interesting.
 * What contract?

Kaito can also Synchro and Ritual Summon.
He's already shown that he can semi-nomi Special Summon and Fusion Summon instead of XYZ Summoning big monsters (though he can XYZ if he wants to). Perhaps he has other tricks up his sleeve. Considering that Synchros are good enough in Real Life to break the game, it's very possible that Kaito will recognize how good they are and use at least one of his own.

Kotori will eventually duel, under possession of a Number.
The Numbers represent the desires of the human who first obtains it. Kotori, despite being part of the Numbers Club, is the only one in Yuma's group of friends who has never been shown to duel. Feeling that the rest of Yuma's friends (Cathy in particular, being a rival for his affection) are more useful than her, she'll attempt to build a deck of her own and her jealousy will result in the appearance of another Number card. (A literal Green-Eyed Monster) She may even become a temporary antagonist like Carly did in 5D's as a Dark Signer.

There will be Number 0, and it will be the most broken Number.
Yu-Gi-Oh has a tendency to do that. Most likely 0 will be a monster with 0 ATK and DEF points but has some really broken powers that make it nearly impossible to defeat.
 * Number 01 will definitely be the best. Comparing 90 with 10, for example, shows that the numbers tend to get better the closer they get to 01. The single-digit numbers (or at least the top 3) could wind up being the "god cards" of the series.
 * Each number could have a Chaos Number counterpart. When Yuma and Astral duel whoever wields Number 01 (probably Dr. Faker), Chaos Number 01 will probably be its One-Winged Angel form.

Zexal is a reboot, existing in a separate continuity from the other three series.
Nothing suggests that any of the previous magic (Zorc, the Signers / Dark Signers, the Crimson Dragon, the Neo-Spatians, Darkness, Atlantis and the Legendary Dragons, etc...) exist in the current continuity. Particularly seeing as Yuma's parents are both adventurer archaeologists, if there was going to be a continuity nod that gave a nudge to the previous series' magic sources, it would've been mentioned by now. In fact, the existence of the astral plane seems to outright retcon the existence of a traditional "shadow realm" as other series have demonstrated.

Also, Kaiba Corp is not mentioned once during the entire first story arc (pre-Heartland-tournament), despite being mentioned frequently in GX, 5Ds, and of course the original series. Domino is also left mysteriously unmentioned.
 * Plus Synchros. I don't think they are even mentioned, despite the fact that they are still incredibly good. Zero Reverse was prevented, thus there would be no reason to outlaw them, and XYZ's aren't necessarily better.
 * Possibly Jossed, since we've seen monsters from DM and GX in episode 15.
 * Maybe the Yugiverse branched at GX - one route was 5D's, and the other route was Zexal.

Utopia will have a fusion form.
Every ace card has had a fusion form so far (Dark Magician to Dark Paladin, Neos to...Divine Neos makes the most sense, Stardust Dragon to Dragon-Knight Draco Equiste), and it would be a shame to waste this tradition. Bonus points for if it's a fusion using Galaxy-Eyes or Black Ray Lancer.
 * It will have the same effect as Utopia, except there's no cost except a once a turn limit. Perhaps it's a fusion between Utopia and any other Numbers card.

Kaito will have a face-heel turn
This is most likely going to happen, like it has with 90% of villains in this franchise, but it'll be because Hayato DIES ANYWAY. This will cause him to BSOD, and eventually go all Roaring Rampage of Revenge on Faker with Yuuma and Astral.

Astral planned the scattering of the Numbers.
Assuming that the top Guess is true, then Utopia must contain Astral's good side. That part took control long enough to set up the events of episode 1. Whenever Yuma defeats and acquires a Numbers card, it is purified. When he gets them all, the expelled evil will take form and challenge Yuma to the last duel of the series.
 * Slightly confirmed as of Episode 37. No. 96 Black Mist is being empowered by the other No. cards. Except for No. 39 Aspirant Emperor Hope; he came to Astral's aid when Astral was assaulted by Black Mist.

Kotori and Mr. Heartland are somehow related.
Their hair colour is near as dammit the same shade and pattern; certainly enough to justify a later twist reveal of long-lost uncle and niece-type relation.

An evil side of Astral, or one of Astral's race, will show up and challenge Yuma at one point
And just for added in joke, his seiyuu will be that of Ankh
 * Already DID show up. His name is Black Mist, he dueled Tetsuo during his first appearance and lost when Yuma lied to him about Tetsuo's strategy.

At one point, Yuma will have just gotten a big win and be bragging about it...
When a mysterious motorcycle rider shows up, challenging him to a duel, either almost winning but stopping at the last second (As in this case, Yuma would be using numbers) or managing to get a spectacular draw against Yuma, warning him not to get too cocky... the rider? Yusei or Jaden, Jaden would make a little more sense in that he has Yubel and no Turbo duel excuse. Yusei could be saved for a final episode duel.
 * The last episode, or an out-of-canon OVA, will include a four-way free for all duel: Yugi vs. Jaden vs. Yusei vs. Yuma.

The in-show fictional character "Dead Max" or something similar to him will appear as a Numbers card.
The Galaxy Queen looked like one of the evil queen from the show, so why not one that looks like Dead Max?
 * Very unlikely, seeing how Numbers take a form defined by the person who first found it. Unless someone else related to the show picks one up, this will not happen.

Galaxy-Eyes Photon Dragon isn't just an Expy of Blue-Eyes White Dragon.
It is Blue-Eyes, in the future. It has the exact same attack/defense/type/attribute/level. It looks very similar. Its name is structured the same way. The only significant difference between the two dragons is that one is a normal monster, and the other has an effect whose only seeming purpose is to counter Xyz monsters.

Somehow Blue-Eyes knew that the Xyz monsters would appear and become a threat, so it transformed into Galaxy-Eyes in order to prepare for them.

Old man Rokujuro is a futuristic Yugi.

 * Based on the fact that a lot of his cards are similar to Yugi's. (Red-Eyes Black Dragon, Polymerization, Mirror Force, the three Knight cards, De-Fusion and Monster Recovery). He also made perfectly detailed statutes of Dark Magician, Dark Magician Girl, Red-Eyes Black Dragon, and Blue-Eyes White Dragon, which would be pretty difficult for someone who'd never seen those cards. (And seeing as there aren't a ton of images of them lying around Heartland, it's probably been a while since anyone has.) Furthermore, consider the strategy Rokujuro uses to defeat Yuma in their first duel: He fuses three Blue-Eyes Statue Dragons together to create Blue-Eyes Ultimate Statue Dragon, with which he destroys Dark Magician Girl, then he uses De-Fusion to turn Blue-Eyes Ultimate Statue Dragon back into three Blue-Eyes Statue Dragons and take the rest of Yuma's life points. This is identical to the move Yugi used to defeat Noah in the Virtual World arc of the original series, when he was dueling with Kaiba's cards.

XYZ Dragon Cannon from the original series will turn out to be connected to the Xyz monsters... and then spark off the beginning of Synchros.
Name's the Same between Dragon Cannon and the Xyz cards... Kinda. Just replace Xyz materials with X - Head Cannon and so forth, and it's a pretty clean parallel in how they work, as well. (Monsters that only configure with each other, can be arranged in different ways, and can have some pretty powerful effects.) Plus, I could see the series of monsters that introduced the concept of sending a series of cards to the graveyard without Polymerization, in turn introduce synchro summoning in-universe. Would certainly be a cool way to tie the timeline together and help it fit. In short? XYZ -> Xyz -> Synchro.
 * That doesn't seem to make much sense. Especially since the original names are completely different (Ekusu-Wuai-Zetto vs Ekushiizu).

Black Mist is the Zexal equivalent of Dark Bakura
I mean just look at him. A recurring  who is a malicious entity from another world, trying   collect the plot coupons for his own ends while he himself is sealed in one of them and is also capable of. Yup, that's Dark Bakura.

Astral is an alien from the dimension where all of Heartland's trash is being dumped.
He was sent to destroy the source of the trash, because it's damaging his home dimension. But by hanging out with Yuma, Astral will realize that this dimension is worth saving and will try to protect both his world and Heartland. Ergo, Zexal's plot is actually more like Captain Planet with Card Games.