The Lorax/WMG

The Once-ler was Ebony's ideal man
- Looks like "a pentagram" of Gerard Way and someone with a rounder facial structure.

- Seems bi.

- Once corrupted, took on to wear Slytherin-ish clothes.
 * Slytherin-ish clothes? Leaving the colour aside, I believe his clothes were more like Willy Wonka's. It does make him look like a snake, though, considering his posture.

The film will have an entirely new ending.
The Lorax will not leave for the last time, but stay and fight the Once-ler's actions once and for all, somehow!

...or, it will preserve the original ending, but tack the new one on after it.
The Lorax leaves and in the present day, Ted is given the last Truffula seed from the Once-ler... but this time, Ted actually DOES plant the seed, and eventually, enough small trees grow to the extent that the Lorax returns with seeds elsewhere, and together, they both plant a new forest.
 * The second trailer does seem to show that a chunk of the film is Ted trying to escape and plant the seed.
 * One trailer also shows the Lorax lifting himself into the sky as the Onceler watches.
 * Confirmed. More events are tacked onto the book's ending, but Ted never meets the Lorax.

As a punishment for screwing over the forest, the Once-ler was turned into a Lorax-like creature.
It would explain how Old Man Once-ler looks in the trailer.
 * Jossed. He's still human.
 * That would have been cool, though.

Ted will become the Once-ler
Then use his machines to go back in time to try and stop himself

The Once-ler is Ted's father or relative
They look a lot alike and this troper is not the only person on the web to think this. Admit it it sounds like a good theory. Maybe the Once-ler was so ashamed at what he did he left and went into solitude. If Ted finds out this news in the film perhaps Ted would go into total shock. There could be a nightmare sequence in which Ted sees the destruction of the trees, or he could be the Once-ler in the dream and has the Lorax yell at him causing him to wake up. The film could end with the Once-ler being redeemed by his son or the Lorax telling Ted he redeemed his family by replanting the trees.
 * This explains why there isn't a grandfather or father present in the trailer.
 * The grey hair may rule out father, but grandfather is a possibility, unless the hair turned grey do to the stress of realizing what he did to the environment.
 * Could explain why the mother and grandmother acted a certain way once the oncler was brought up at dinner. Bitter feelings come from the mother because he left them, but grandma always had a soft spot for him.
 * Ted's Grandma does seem to know alot about the Once-ler.
 * There's also the way Grandma strokes the living seed, saying "I remember you!"
 * The younger Once-ler had noticeable freckles. Ted's Grandma doesn't, but Ted's mother and Ted himself both have freckles as well.
 * As TheSassyLorax points out, if Grammy Norma is old enough to remember when there were trees everywhere, why doesn't she simply tell Ted what happened to them? Why send him off into the dangerous wastelands outside of town? Unless she had another reason, such as sending him to meet his grandfather...
 * But if she wanted him to meet his grandfather, why didn't she go out herself to bring him into Thneedville? Why have Ted do it?
 * On an interesting side note, Betty White supports Norma/Once-ler

Why the Once-ler wont care about the environment

 * The Once-ler was going to listen to the Lorax but then and the Once-ler won't care what he has to say and therefore the crapsack world.
 * Close.

The Once-ler will be redeemed at the end of the movie

 * Confirmed. In fact, he's more sympathetic overall.

The Once-ler founded the corrupt government seen in the second trailer.
] And possibly the leader is his son or one of his many many relatives (though that part's not necessary for the WMG). Oncey saw the error of his ways as an old man but the leader exiled him to stay in power and prevent people from finding out. If the leader's his relative, he disgustedly disowns the old man for going back on the things he'd ingrained in the relative as good and true.
 * Jossed, sort of. His own thneed business grew the town it is today, but it went out of business, and the town is now governed under O'Hare who had nothing to do with Thneeds and got an idea of how to become a zillionaire on his own.

The Once-ler becomes an embittered, cynical shut in disease and ravaged by the pollution he created.
It would explain why we see his face as young guy and not as an old man, since the original purpose was to take away his humanity so he could be a symbol instead. I haven't read the book or seen the animated short in a long time so I don't remember if this already happened in them. I think the Once-ler was coughing and in wheelchair at one point in the short though, supporting the idea.
 * He was never in a wheelchair, just in a chair with wheels. And the Lorax was coughing, not the Onceler. Doesn't joss this theory, though.

O'Hare will be an Anti-Villain

 * Going with another poster, O'Hare is a relative of the Once-ler. He's ashamed of what happened, so he hides it from Thneed-ville and won't let anyone leave. If they do, they might meet the Once-ler who will tell the story and shame him out of power
 * Nope, the film shows he's a villain through and through.

The Once-ler's family deliberately sabotaged his business.
Why? Good ol' Envy and Tall Poppy Syndrome. His achievements benefitted them, but because it was him, they were jealous and wanted to see him fail. Hence his mother's manipulation and the insanely self-destructive policies they pushed.
 * Makes sense actually. That might be the reason why they advised him to chop down the tree instead of simply finding a device to harvest only the leaves- which is the only part of the tree they used. That would be less destructive for both the business and the environment.

Audrey and Ted won't get together.
She's a good 4 or 5 years older than him, which is a big difference due to them being kids. Plus, while Ted is striving to make her fall in love with him, Audrey likes him more as a close friend- she was speaking half-heartedly when saying she would "marry him on the spot" if a guy found a tree for her. Once they discover it was a May-December Romance, Ted will realize it won't really work out.
 * That's no fun.

Whimsy Words
When the Truffula tree's were compared to being softer then silk and like honey, neither Ted nor Audrey understood it. Why? Because everything in the city is artificial. Silk and honey are both naturally occurring events.
 * But then, why do all the citizens seem to know that trees produce air for free, and that Audrey (at least) knows about photosynthesis?
 * They didn't. Audrey and Ted both had to tell them that trees produce air for free, and only Audrey really knew about photosynthesis- and that was from a book (or equivalent). Only the older people would know about trees, and it seemed like Gramma Norma was the only old person in that town.

The Once-ler actually did have a decent life.
Perhaps after his business failed, he didn't become a shut-in right away, and instead lives his life for a while, making friends and playing music (as young people do). Eventually his guilt did consume him and forced him into hermitude, but that doesn't mean he couldn't have actually had a life beforehand. It's heartbreaking to imagine he became a recluse immediately after he "learned his lesson", and never gets a second chance before he was already in his golden years.
 * Makes me kinda wonder where he's going to make friends from since everyone left already...
 * Human friends! He still has to eat, he could have made them on his way to the store for all we know. Maybe he travels into the city for poker nights or something. He doesn't seem to live very far.
 * He may actually not be that old. He was probably in his early 20s when the events of the Flashback took place, and the film shows O'Hare looking roughly the same as he did when the Onceler's factory went under. That would seem to indicate that only 25-30 years max have passed since then, which would make the Onceler roughly 50, and prematurely gray.
 * It does make sense for him to grey prematurely, between the pollution and his guilt.

Brett and Chet are inbred.
They are arguably dumber and more Seuss-like (non realistic) in appearance than any other character in the film. We never see their (or the Once-ler's, if this WMG is true) father. This might explain why the only family members the Once-ler invites to help with the business are the ones we saw him living with before. They're the only ones who'll still talk to them after the Once-ler's mom gave birth to the results of an incestuous union.

Brett and Chet are not The Once-ler's brothers.
Come on, they're the spitting image of Uncle Ubb, only taller.
 * Yeah, while I was watching my guess was that they were his cousins, until Once-Ler's mother declared that Brett was her new favorite child. Then again, maybe that makes the sting worse: she's picking her nephew over her own son.
 * There's also option two; they are her children, either Once-ler's dad died or his mom just betrayed his dad with his uncle; making Brett and Chet his half-brothers.

Book!Once-ler's motivations might have stemmed, not only from his greed, but from his father.
When the Lorax came back for the third(?) time in the book and scolds him for what he's done to the fish and birds, the Once-ler outbursts with the phrase "Now listen here, dad!", going on a tangent on how he's telling him not to do this, and that, and you're hurting others, and blah blah blah. He also tells him that he'll keep doing what he's doing, whether the Lorax likes it or not. His trying to make a big buisness in manufacturing Thneeds could be a way of trying to prove his dissaproving dad wrong; he'd be rich, successful, with people benefiting from his actions, everything his dad said he wouldn't.
 * Also, in the book, he invites his brothers and all his uncles and aunts, but not his parents, to join him in his success.

The Once-ler was hit by a falling tree.
The Lorax says that a tree falls the way it leans. The first tree he cuts down leans over him. Make of that what you will.

The Once-ler isn't Camp Straight.
He seems very girly:
 * the pink apron
 * the bunny pjs
 * watch the scene where the Lorax and animal friends invade his house.
 * there isn't a real love interest for the Once-ler.
 * his reassuring himself that "knitting is totally manly"
 * maybe why his mom is dissappointed in him
 * Um, that's kind of the definition of Camp Straight, or at least Ambiguously Gay or something. Plus his mom may be disappointed in him only because she thinks he's gay because of his more feminine habits (Knitting, pink apron, etc.) Like you said, he was never given a love interest; he could be Asexual for all we know. Plus, how would the scene where the animals invade his house indicate anything? I think most people, regardless of orientation, would probably scream and freak out at finding a small, furry orange-man-thing with a huge mustache in thier bed and then try to get all the forest animals the Hell out of thier home. To my memory, there wasn't anything indicating of his orientation in there except that maybe he wasn't too thrilled at finding the Lorax in bed with him.

O'Hare's goons are Brett and Chet

 * Highly unlikely, unless they changed their names. Their names are given as Marty and Mc Gurk.

The moral of the lorax is also the same one as "The Princess and the Frog"
About needing instead of wanting, Once-ler wanted his family's love and his success, what he **needed was to take care of the environment...unfortunately he learns that on late, and Ted wanted Audrey as his girlfriend what he needed was to care about the trees, only when they get taken "Part of the way."do they get what they need instead of what they want. Its how the Lorax's magic works, his magic can only take you part of the way, you have to find your own happily ever after.

The people who made Once-ler's character design from the animated were sexually attracted to him.
The animators obviously put in a lot of specific non-sexual kinks into the character that give his movements and design a really really slight but still present sexual turn to them. For example, his regular suit and green suit: both have a very obvious, to those who are familiar with it, suit fetish. From the plain vest/dress shirt/trilby combo to the full on tailcoat, which is very very popular with suit fetishists and the care given with the way the coat moved. Also, his posing and movements also have enough attention and affection in them to make him likable despite destroying the environment and being the bad guy. The camera angles that make him menacing, combined with his lankiness is enough to give him a really really appealing look to him. His nice movements are very smooth and relatable when he does anything silly or sad, looking often like a kicked puppy or a happy puppy, but he gets very adult and authoritative when he goes into megalomaniac Once-ler. This is why the Once-ler fandom-within-a-fandom even exists; because the Once-ler's creators made him sexually appealing and the audience is picking up on it.
 * Are you sure you're not one of those crazy Once-ler fangirls?
 * Can't it be both?

Ted's grandma was the girl to recieve the first thneed.
She mentions being around the see the trees, and it seems like the only people who spent any time in the forest were the Once-ler, his family, and the mob of people wanting to buy thneeds.

The proper name for a baby bar-ba-loot is puppy.
Thus explaining "Just look at me petting this puppy."
 * I believe he's referred to as Pipsqueak twice.
 * I think what the OP means is that baby bar-ba-loots are called "puppies" instead of "cubs." Like how baby skunks are "kittens." That particular one is named Pipsqueak, but he's a puppy. Like how you can name your pet cat Fluffy but it's still a kitten if it's young enough.

Audrey is related to the Once-ler.
She has long legs, a lanky physique, and freckles, all like the Once-ler. Her red hair, however, comes from his mother's side of the family; The Once-ler's mother has blonde hair, and Grizzelda, his aunt, has red, which is a mutation of the blonde gene.

Audrey is the Lorax.
Well, she has orange hair, green eyes. She adores trees and would do anything to get to see one. She more or less speaks for trees and she knows exactly what they look like.