Here's some of my ideas for KH3 which would go on PS3:
*Sora, Kairi, and Riku as the main characters. You can choose whoever you want to play as and anytime during the game you can switch back and forth on who want to be.
*New Disney Worlds: Robin Hood, Camelot, Hunchback of Notre Dame, Great Mouse Detective, Narnia, Gargoyles world, Toy Story, A Bug's Life, Wind in the Willows world( Toad), Snow White world, Cinderella world, Sleeping Beauty world, 101 Dalmation's world, Black Cauldron world, Jungle Book world, Brear Rabbit world( replacing Winnie The Pooh as the mini game world), Incredibles world( have Sora, Riku, and Kairi in superhero like outfits), Finding Nemo World, Pocahantos world, Emperor's New Groove world, Treasure Planet world, Atlantis The lost Empire world, Dinosaur world( have Sora, Riku, and Kairi transform into dinosaurs to fit in).
*6 returning worlds that are a whole lot bigger than before: Hollow Bastion, Disney Castle, Destiny Islands, Neverland, Wonderland, and Olympus Coliseum/Greece
*5 fresh original worlds
*Worlds from other Square Enix games: A Star Ocean world, a Musashi world, a Dragon Quest world, a Full Metal Alchemist world, a Grandia world, Xenosaga world, Valkrie Profile world, Vagrant Story world.
*A new main villian who is a young keyblade master( slightly older than Riku) that can control the Heartless and wants to deeply kill Sora, Riku, and Kairi. His followers are evil keyblade masters who keep opening up the keyholes so the heartless can destroy the worlds.
*A love triangle between Riku, Kairi, and Sora to make the storyline even more interesting( meaning that Kairi has to choose between Sora and Riku).
*New reaction commands, abilities, keyblades, and magic.
*New summons including FF summons.
*The same FF characters from the previous games return and several more appear in Hollow Bastion. Plus have several FF villians including Jecht and the Judges.
*Long cutscenes with a few exciting AC style cutscene duels.
*All the cutscenes have the same graphics as the FMVs
*More mini games including a motor boat racing competition on Destiny Islands
*Have the option to change clothing and armor
*The timeline for the game is when Sora and Kairi are both 18.
*A bitter rivalry between Mickey and Mortimer. This part is just a side story. Have it where Mortimer is one of the evil keyblade masters.
*Try to have the game rated T.
*Xenahort returns in some form. He's not the main villian but his story arc ends in the game.
Well, those are some of my ideas for a KH3.