The Princess and the Frog: This world could be a bizarre mix of the bustling city and swampy beau's. Sora and the other playable characters could will likely be turned into frogs. This will make the interactions between them and Tianna and Naveen easier. Dr. Facilier would make a fine boss and the friends on the other side could be re-written as heartless. In another change from the movie, Facilier could promised the friends the hearts of the people of New Orleans instead of their souls to keep the KH mythology going. His boss battle I imagine would be similar to Jafar's battle. In that you target an object instead of the foe, in this case, Facilier's voodoo charm. Once it's gone, the friends can take it from there. Plus, Tianna is a candidate for being one of the Seven new Princesses of Heart.
The Black Cauldron: I know this was Disney's biggest flop, but as of right now, it's my favorite Disney movie. The Horned King would make a perfect boss and both he and the villain of 4 could be searching for the black cauldron. The cauldron-born, though they got very little screen time, could be remade as nobodies and mooks. Plus, the hero's would be of great asset, with Tarren's providing physical support via his sword and Elonwy providing magic support via her baubel. Terran's decision to give up a hero's life at the end could create a moral conflict within Sora and the others on wheather or not they should continue wielding keyblades when it's over, or seek a normal life in the end. And Elonwy is a very underrated princess. Sure she's no fighter, but she helped Tarren escape the dungeon and is a no nonsense character who always speaks her mind. This could make a her a canidate for one of the new Seven Princesses of Heart
Any dog movie(The Lady and the Tramp, 101 Dalmations, Oliver and Company, The Fox and the Hound): Any of those movies could reflect a theme of KH. The Lady and the Tramp could reflect Sora and Kairi's growing feelings for each other if Enix decides to put a romance in 4. 101 Dalmations could reflect family, which has been neglected in KH too often. Sora and the others realize they have families they have ignored for too long and need to put family as priority. Oliver and Company could reflect the need to protect home and hearth. Sora and the others realize that they have been away from Destiny Islands for a long time and begin to grow homesick for it. The Fox and the Hound could reflect friends parting ways.
The Jungle Book: Nomura has wanted this movie to appear in KH for a long time. And though I've lost interest in it, I could see it work. Unlike Deep Jungle, this one could be more on the ground and have more characters to aid you such as Mowgli, Bagheera and Baloo. One challenge would be fitting in the various locations in the movie into the map, so they may have to pick some but not all. Plus, maybe Enix could throw in a small inside joke where Sora says Mowgli sounds sorta like him, then quickly dismisses the idea as stupid. A reference to the fact that Osmond was Mowgli in that stupid Jungle Book sequel.
The Rescuers Down Under: Growing up, The Rescuers Down under was my favorite Disney movie and I owe much to it since it spawned my desire to help wildlife and nature. I've always felt Kingdom Hearts needed that theme. In order to fit it in KH, maybe the next villain seeks Marahute for some mysterious reason and are using Mcleach as a pawn to find and bring Marahute to them since in the movie Mcleach wanted to make money of the eagle. The only challenge would be should Sora and the others be turned into mice or remain human in this world, or should it be different for each playable character? Needless to say this world could really show off the beauty of Australia's wilderness and show how precious nature is. Mcleach could even become a heartless in his boss battle because of his greed.
Zootopia: Sora is turned into a humanoid animal here, and we learn that instead of being turned feral, Zootopia carnivores are being turned into Hearltess and Nobodies even though they have not succumbed to their inner darkness. However the world plot is be set after Zootopia like with Monsters Inc and Big Hero 6. Bellweather has escaped from jail with help from the new villain, and has merged the Howler Virus with Darkness and is using it to turn Carnivores Heartless. Or perhaps the game plot would follow the plot of the movie. Regardless, Sora helps Judy and Nick solve the mystery
Brave: As a... well brave princess, Merida is a canidate for being one of the Seven new Princesses of Heart, and if a major theme in KH4 and the next saga is free will vs destiny, this could be what Sora needs. Mor'du also fits well into the mythology, as his lust for power destroyed the bond between him and his brothers. Maybe instead of being turned into a bear, he's turned into a heartless.
Movies from companies Disney has bought(Excluding Star Wars and Marvel)
Anastasia: If the theme of memory returns in the next saga, this could fit perfectly. Through in a game universe reason, Sora runs out of Muny when he arrives and in order to keep upgrading, he reluctantly agrees to help Dimitri in his con, unaware Anya is Anastasia, and that he's just made himself an enemy of Rasputin, who is re-worked into making a deal with the Realm of Darkness, since it's the Hell of KH. Plus Anya is a canidate for one of the Seven Princesses of Heart. And before anyone throws fusses about history, this has one life line that Pocahontas does not. No one knew what the real Romanov princess's fate was, not until the early 2000s.
Avatar: A good replacement for Pocahontas would be this world. True the plots are similar, but it has one lifeline Pocahontas does not. No one is based on history. That said, like Monsters Inc and Big Hero 6, the plot of this world should be set AFTER the movie. Upon arrival, Sora realizes he has been turned into a Na'vi and can speak their language.(Na'vi was developed by an actual linguist and has enough words and grammar rules so that you can actually speak it), and finds it under siege from Heartless or Nobodies armed with assault rifles and war machines. Not only that, but even Pandoran wildlife have been turned into Heartless and Nobody. Sora meets Jake and Neytiri and learns that the Heartless are searching for "The Tree of Hearts", which is the worlds Keyhole. Along the way, Sora goes through his own spiritual journey and has visions from Eywa. Plus, Neytiri seems like a good canidate for one of the Seven Princesses of Heart.