We know that it is a Disney world. We have left the Classic Disney Villians and Summons worlds. I did a whole logic on this in the Rumored Possibilities thread, but, basically, I showed how Black Cauldron and The Emperor's New Groove were the only likely worlds. (Maybe Lilo and Stitch, but due to how the movie operates, it would either be Gummi Ship or 101 Dalmations related: either a hidden boss in space or a collect all the experiments type miniquest, not a whole world). Wonderland, and possibly Pleasure Island are the only real options for returning Disney worlds, as well.
About the summon worlds: if they did Bambi, they would have to have a Heartless boss, and no real storyline, and if they did Dumbo, the same thing would be true. Cloud's already going to be there, as well as Mushu, Simba, and Genie. (Neverland might return for Tinkerbell, <since the summon worlds are supposed to appear> but there is already a pirate world, and according to Nomura, he doesn't do two worlds with the same theme in the game. It might do actual Neverland, though, but it would still be odd.
Basically:
Possible Returning: Wonderland, Pleasure Island, Neverland
Possible New (only 1): Black Cauldron, Emperor's New Groove
or
Possible do it like Monstro worlds (madeup story, boss): Great Forest (Bambi), Circus (Dumbo)
I don't think Black Cauldron will be there unfortunately, since it doesn't seem as humorous as the other Disney movies were, and is on the whole, a pretty dark film. It would be cool though, maybe like a new Hollow Bastion (next to last world, closest to the heart of darkness).
For Fantasia: I don't really think it could work even like Monstro, as the characters don't really work. It's either to real, or not real enough. It might make bit appearance in some level like End of the World, though, but I don't see how they could make it into a world.
Rejoice, though! They have remade Atlantica, knowing that we hated it, with the thought "well, they'll hate it anyway, might as well make it into a joke world" and made it a dancing world! Cower Ursula, or we'll bust-a-groove! What now?!