For me, I would really like to see an updated Pirates world, featuring Davy Jones as a bad guy (come on, he's perfect! He has no heart!) and the Kraken as a boss fight. Treasure Planet would also be interesting to put into the game, even though the movie didn't get a very good reaction from the public. They could probably pull off a few Pixar worlds as well, such as Monsters Inc. and the Incredibles. Some wouldn't exactly work out, but there are a few that would be interesting.
What do you think? Discuss!
Even though it would probably be a fantastic game, I really don't think that a 3rd needs to be made. KH2 didn't exactly end in a cliff-hanger like the 1st one did... they got a note from the king. It could lead into another game.... or it could just be a simple thank you letter. What else is there to tell? Sora and his friends are back home, evil has been destroyed. There isn't much more too it. If they create too many sequels for the fans, the franchise will eventually grow stale.