Treasure Planet, definitely.
Port Royal, using the plot of Pirates of the Caribbean 2 (and possibly 3, since I don't see them leaving that kind of major cliffhanger in something other than the main plot), of course.
Narnia, for sure. That movie/book is simply too awesome to leave out. Imagine taking on the White Witch's entire army! There is so much they could do there.
Notre Dame/Paris: I would simply adore a world that included Notre Dame. ^_^ Can you imagine a giant climatic battle on/around ND?
Sherwood Forest, anyone? Robin Hood is practically tailor made to be in Kingdom Hearts, complete with giant athropomorphic, clothes wearing animals!
Atlantis, I see getting in, if only because Disney is running out of worlds that are compatible with KH. ;D But it would definitely have enough opportunities for action and adventure.
London: I mean, I'd love to see Basil make an appearance, but I'm unsure of how they'd manage this one. Also, it seems like it would ruin the story to have all three of the main characters running around after Basil... maybe if it was just Sora, then... definitely. ^_^