I'm thinking the roster of worlds will be something like.
Hercules
Toy Story
Tangled
Big Hero 6
Disney World #5
Disney World #6
Disney World #7
The Mysterious Tower/Twilight Town
Radiant Garden
Destiny Islands
Some Endgame World
Of course some worlds will be fairly small but I can see them hitting about a dozen different locations.
My nostradamus prediction before has been 7 disney worlds too. If you put a gun to my head what the whole game would consist of it would be:
Announced:
Big Hero 6
Hercules
Tangled
Toy Story
Twilight Town/Mysterious Tower
Unannounced:
Frozen. I cannot imagine a situation where it isn't one of the worlds. It's too popular, released at a too convenient time to KH3 developement and winter world is a stark contrast to anything other KH3 thus far that have a very much summer feel to them.
Disney #6. This is a bit harder to quess but I think there will be one more returning world beside Hercules. And I think it has a decent chance of being Aladdin (cue the boos).
Like Hercules it's one of the series staple worlds, very popular movie, very easy to implement to KH with the action adventure theme. And most importantly they can keep it fresh with implementing the third movie and having less focus on Agrabah. Or they could do something completely original and the characters would work just fine.
If for some reason it's not Aladdin another possibility that comes to mind is Pirates.
Disney #7. Could go two ways. If they get the permission for it despite EA shenanigans and Disney is cool with it I think it will be Star Wars. First and foremost it's too big of an IP for Square not to use it if given the chance. Secondly it's another world that fits too easily due to action adventure roots. Thirdly it fits the "surprising" world slot.
If they for some reason are denied Star Wars it becomes much harder to predict. It could basically be anything but I suppose two worlds come to mind. First off Treasure Planet due to Roy being somewhat on board with implementing his other 2 movies to the game. The only reason going against this is that TP is one of those movies Disney and Square probably don't particularly care about pushing.
Second one being Jungle Book since they have tried implementing the world before but my big problem with it is that they would need to strip a ton of gameplay mechanics away akin to Lion King world in KH2 if they went with animal forms and who knows if they want to deal with it now that the worlds are longer. I suppose they could do some unique new stuff for lion form. But really this last world could be almost anything and it wouldn't surprise me. Maybe they want to have one old Disney flick to balance out the new ones like Robin Hood or (please god) Mouse Detective.
As for unannounced original worlds:
Radiant Garden. It's been the most common original world in KH wether it's Hollow Bastion or Radiant Garden. I think it will have some small role to play.
Final World. I assume this is some fucked up version of Daybreak Town summoned by MX at Keyblade Graveyard or something. Too much work done modelling the town for XBC for not to use it.
Thats pretty much it. I think Castle Oblivion, Disney Castle and Destiny Islands will have a non playable role or something really bite sized not to really count as a proper world.
Wildcard: Winnieh the Pooh. I'm 50/50 on it returning. If it does it'll be much smaller scale to other Disney worlds and is a minigame hub like before.