Well I think most of my choices have been said already.

My favorite world up till now has been Twilight Town. So, I'd love to see that make a comeback along with Roxas and Naminé.

Honestly, I'm really mad that Frozen came out as late as it did, because now its probably too late to base a world on it. 

deg2000 : I couldn't agree with you more! I'd love to see anything relating to The World Ends with You in Kingdom Hearts. (I know DDD has them in it, but I haven't been able to get it yet.)

Other worlds I'd like to see:
-no.. Wait.. That's all I can think of at the moment.

I'd like to visit the forest/Powhatan village that Pocahontas was from.

I would definitely want to keep going to Agrabah, Halloween Town, Port Royal, Space Paranoids, Timeless River, Neverland, Olympus Coliseum, Any of the town worlds, and Radiant Garden. For new worlds, I would want to go to a final fantasy world that is composed of things from all the main FF games. You would encounter characters like Firion, Cecil, Vincent, Red XIII, Rydia, and many other characters. I would want a boss fight with Garland, who later comes back as Chaos, and a priority boss fight with Sephiroth. The exclusive party member of the world would be Warrior from the original FF with something like his Dissidia design because i think best represents the series. A world based of the world ends with you would be nice, being able to fight reapers alongside Neku. For boss fights I would want Megumi Kitaniji in his Draco Cantus noise form, and an original boss based on the game. For new disney worlds i would want: Bambi, The Sword in the Stone, Pocahontas, and Toy Story. a world based off Studio Ghibli films would be nice too.

I would want to use some of the ones already in previous titles, of course... Here's the towns I would want:

Worlds that I really want to return:

Twilight Town/Traverse Town - Maybe they could be the same world, but both be accessible through a portal or something.
Neverland - This was one of the coolest worlds in the original game. I was sad to see it go.
Radiant Garden - This was an awesome world in KH2. Maybe in KH3 they could make it available for you to go to Hollow Bastion?
Olympus Colliseum/The Underworld - This has gotta return. I prefer the KH2 version because of the Paradox Cups.

New worlds:

Andy's House (Toy Story) - Fun Fact: Woody and Buzz were going to be summons in the first Kingdom Hearts, but they were scrapped. This would be a cool world, and maybe Sora, Goofy, and Donald could all be more toy-like in texture/graphics.
Maybe a world in Frozen...? - ?
Notre Dame - The Hunchback of Notre Dame was a great older Disney movie. This would be perfect for a Kingdom Hearts world!
Atlantis - THAT WOULD BE SO DANG COOL!!
Pocahontasland - That would be cool...

TheFadedWarrior : Haha, yayyyy.. Somebody else said Pocahontas!!! I think it'd be cool to go up against Governor Ratcliffe!!

I would like to see a world based on the Great Mouse Detective and Oliver and Company as well as many returning worlds, especially The Hundred Woods, it's been my favorite world every time.  Personally I don't think any Marvel or Star Wars worlds would work simply because they are honestly too large and have too much history to be properly represented.  I think that a world based on Indiana Jones, if handled properly, would be very interesting

I'm definitely not going to be the first or last to say this but I really want a star wars world. It looks like it's possible that it might actually happen as well as it's been said they're thinking about it (And I would also like a lightsaber keyblade with that please). Some other worlds I think would be cool is A Notre dame world, Frozen world, Wreck it Ralph world, Toy Story world and perhaps maybe even a marvel world of some sort.

And while it would probably be a long shot I think a Emperors new groove based world would be awesome as it's one of my all time favorite Disney movies.

I'm probably forgetting a bunch of worlds aswell.....Dammit there's so many disney movies which you could make awesome worlds out of.