A leaked Disney newsletter included a small piece about the game, at least before the leak was fixed. But apparently they underestimated the internet (always a big mistake), and the information is still around.
Unfortunately, there wasn't a whole lot said about Epic Mickey 2 other than the fact that it does in fact exist, and will be released for not only the Wii, but also the PS3 and Xbox 360 sometime in Fall 2012. The little bit of information we got about the story is that Mickey has once again been tossed into a world full of lesser-known Disney characters. Also of note is that this time around, Oswald the Rabbit is not only on your side rather than being an enemy, but also able to be picked up by a second player for some lightning-based assistance. Oh, and he can fly.
Lastly, the decisions you make in the game do actually change the ending this time. Unlike Epic Mickey, choosing good or bad actions, such as having to decide to destroy or befriend you enemies, will actually make a difference in the ending. Which, depending on what kind of gamer you are and how many endings there are could effectively double or triple the amount of time you put into the game (yes, I'm looking at you 100% completion-obsessed ones).