There was another thread like this not too long ago and I love the idea of conceptualizing new Disney worlds. These are the ones I came up with. I hope you like them!
Woodworker's Village: A Pinocchio (1940) centric world that showcases Gepetto's workshop, the town, the marionette theater with Stromboli's trailer, and Pleasure Island. The "trust" theme circulating in this game would be put to the test with Riku receiving advice from the not-so-honest Honest John. Boss: Stromboli. Heartless: Marionettes.
Windy Willows: One of two worlds centered around The Adventures of Ichabod and Mr. Toad (1949). Features Toad Hall and its surrounding areas. The protagonist(s) that visit this world will learn the strengths and hindrances that are brought on by immense wealth. Possible sub-bosses: weasel gang.
Sleepy Hollow: The second of the worlds centered around The Adventures of Ichabod and Mr. Toad. In this, Sora/Riku have conflicting ideas of how Ichabod can win over the lovely Katrina leading to pondering about Kairi and whether there's someone out there for Riku or not. Having made friends with Ichabod, Sora/Riku accompanies Ichabod home, but they're confronted by the boss- the Headless Horseman. Sora/Riku defeats the boss, but Ichabod mysteriously goes missing. Is he dead or alive?
London Flats: From One Hundred and One Dalmations (1961), Sora/Riku reunites with Pongo and Perdita who are once again dalmatian-less. They infiltrate Cruella's hideout and deal with Horace & Jasper, and later a boss heartless lured by Cruella.
Royal Heights: The Sword and the Stone (1963) world. Sora/Riku reunite with Merlin in his origin residence and seek his guidance in whatever the hell the two are journeying for. Merlin's magic turns Sora/Riku into various animals to help rid Royal Heights of its heartless underwater and in the forest. Afterward, they face off against the boss, Madame Mim. Her boss fight is similar to Pete's from Timeless River, but instead of the location of the fight shifting, Mim changes animal forms after registering a certain amount of damage until finally turning into a purple dragon. Also, Royal Heights will replace Olympus Coliseum and the Mirage Arena with a Tournament Square where the recreational battling will take place. Also, in lieu of tournament trophies, ranks of Knighthood will be achieved.
Deep Jungle: While the land is already a world Sora has visited, this time Sora/Riku lands on the complete opposite side of the world: miles and miles from anywhere else. Here, Sora/Riku encounters character's from The Jungle Book (1967). They help aid Baloo and Bagheera steer Mowgli home, but find themselves tangled in altercations with antagonists King Louie, Kaa, and Shere Khan.
Devil's Bayou: Centered around The Rescuers (1977). Sora/Riku hear a rumor of a jewel that grants great power to its owner, the Devil's Eye. They go on the hunt for the jewel, but instead find a letter in a bottle from Penny and two mice, Bernard and Bianca. After talking with the mice, Sora wants to help free Penny while Riku wants to find the jewel. They go their separate ways. Sora battles against alligators Nero and Brutus and saves Penny. They reunite with Riku who finds the jewel, but discovers it is powerless and the rumors were false. It's only an object of wealth. Upon exiting the cave, Riku endures a boss battle against a gun-carrying Medusa and a heartless she lured there. After the battle, Riku chooses to bestow the jewel to Penny, knowing its wealth will help her down the road.
Land of Opportunity: Obviously eastern-America from Pocahontas (1995), Sora/Riku help Pocahontas and her relationship with John Smith while evading Chief Powhatan's ill opinion of them and Governor Ratcliffe's lack of trust in them. It becomes apparent that Ratcliffe is merely a heartless pawn and becomes a boss of the world.
Giant Peach: Appropriately from James and the Giant peach (1997), Sora/Riku arrive on the midair peach and help its inhabitants with chores around the vessel brought on by various mini-games like Hundred Acre Wood. Also like that world it has no heartless and no boss. Whilst on the peach, Sora/Riku understand the importance of team work and community and think of what's going on in the lives of Selphie, Tidus, and Wakka back on Destiny Islands.
Parisian Cathedral: From The Hunchback of Notre Dame (1996), Sora/Riku help party member Quasimodo save Esmaralda from the clutches of Judge Frollo who has also lured the heartless to the world with his dark ambition.
Incan Kingdom: From The Emperor's New Groove (2000), Sora/Riku stumble upon Pacha and a llama trying to make their ay to the kingdom's castle in order to restore the llama back to the emperor. They take up their cause and journey with them through the kingdom's treacherous trail leading up to a boss battle against an experiment that villain Yzma conjured up.
Atlantis: Appropriately from Atlantis: The Lost Empire (2001), Sora/Riku help Milo explore the world and end up facing a heartless lured to the world by expedition leader Rourke.
Bayou Hills: From The Princess and the Frog (2009), Sora/Riku arrive and change to animal form to help Tiana and Prince Naveen (as frogs) in their request to become human again. However, the evil Dr. Facilier uses his batch of evil spirits and illusions to drive Sora/Riku apart, leading to a boss battle against him in the conclusion.