This is my speculation after watching the trailor, I haven't looked at anyone elses theories yet, so I'm sorry if people have already said these things
Well in the promo it shows Riku fighting Zexion, and Zexion appears to be using Soul Eater. But Zexion is also shown using a book, so I'm guessing he can mimic other peoples weapons, not sure how that's a spoiler though. Also from this promo vid it shows Sora fighting in different costumes, like a black santa suit for halloween town and his outfit from KHI, so I wonder what kinds of things you need to do to unlock them. And Sora is shown wandering around a place that looks like castle oblivion and fighting the Organization members from KH:CoM, except with KHII fighting, so it looks like they will be adding castle oblivion to the worlds. Then it looks like they are bringing back the mushrooms from KHI, at least the black ones. But the best part was when it had the english voiceover for one of the new scenes, which means, it's most likely going to be in america and europe.