Basically, they point out a number of 'weird', small events that are never explained. The most interesting of which being:
- Xigbar's cut off line at the end of Olympus
- Riku's sudden haircut, and the similarities that scene has to dropping from DDD
- Kairi's death resembling Xion's, also no heart escapes from her
- DDD-style keyholes and portals
- The watery Darkside with the cryptic gummiphone entry
- Characters in the end scene appearing to stare not at Sora and Kairi, but something else - with the exception of Roxas, Xion, and Namine.
- Other minor things: Sora allegedly using a DDD move to teleport to protect Riku against Aqua, Kairi's costume resembling a Chirithy kinda, using reality shift, etc.
The theory holds weight because KH has already pulled this stunt, in both KHUx and DDD. I wouldn't put it past Nomura to pull something like this, except that it seems unfathomable that they would end a game without revealing it, even for Nomura. A big problem is that while Sora and Riku could've made it to the Sleeping Realm, were they the only ones saved? Did they somehow pull in all of the other Guardians of light? Anybody left outside in the original worldline is dead. Did he specifically save every character in the whole universe, or did some Disney characters get vaporized? This is my biggest problem with the theory, they gave interesting answers for the little discrepancies, but their big picture timeline doesn't seem to hold up.
My thoughts on the other things:
- Xigbar - It was a weird scene certainly, but it could either point towards a greater conspiracy, or simply as foreshadowing for him being Luxu.
- Riku's hair - I like this explanation because it's the only one where Riku's sudden haircut is actually given any explanation at all.
- Kairi's death - I think more so than the other events, this one is actually supposed to be mysterious. Her death and return is very cryptic, she apparently isn't dead because Sora knows how to save her; a thought hes never had for any other character. I hadn't caught the weird Darkside entry, and like how it connects with KH1 symbolism, but it makes little sense that that's her. Also, I went back, and she definitely swallows the paopu fruit, so that whole section is bunk. The Xion connections are interesting, we'll have to see.
- DDD portals and keyholes - I noticed this my first playthrough as well, and chalked it up to 'gameplay stuff'. We do see a DDD portal and keyhole in the real world - when Riku is preparing to dive in and save Sora, and the keyhole at the end when Sora goes to say goodbye to those stupid dream eaters. I don't know about this, I think it might just be how keyholes look going forwards, they were different in KH2 than KH1, so this might just be how they are now.
- Characters staring not at Sora - I think this is just a weird camera angle. Donald and Goofy seem to point off and try to run towards the paopu tree before Mickey stops them. In any case, they see something exciting enough to try and happily go to it - I don't think 'weird shit on horizon' would get that response.
- The link block move and reality shift - If this theory is true, than this would be a clever indication. The link block move would be a nice touch, but Sora seems to give Eraqus' keyblade credit. The reality shift Sora/Riku move could also just be a new gameplay thing.
In the end... I don't know. I got excited reading through the theory, and their explanations for the little things is neat, but it would be such a big twist, I just can't see it happening. I'm curious to read other people's responses.
