I'm open to whatever they're doing with the Sora and Riku in Tokyo game. I'm keeping my expectations down, but at least Riku will be playable. But what I'd like to see in the series beyond that, in KH4 or whatever....
I'd like it if keyblade transformations functioned less like form change/link styles and more like trick weapons in Bloodborne, where you can switch into em on the fly, and switching back and forth from key to whatever mid-combo is it's own attack. Of course, they'd be more comparable in size and execution to the regular keyblade than the gigantic KH3 tranformations.
It would be neat if there was a little Zelda-style puzzling (like magic in KH1), where using certain transformed keyblades would open certain paths or destroy certain bosses.
I'd prefer form changes, links, attraction flow, free run, flowmotion, and air step essentially scrapped, with shotlock relegated to a particular summon or limit (minus the lock-on beeps), because it's pretty at least. I don't ever want to see the command deck again, but more customizability with combos would be cool. I'd like drives and summons back and expanded. Or something new, if they have a better idea. I feel MP Charge has run its course. I liked keyblade attacks charging magic in KH1.
I think the way Sora or whoever moves around the field should feel smoother, and more tactile. Sora should be able to run on and bounce off of walls anywhere, but it should feel like the player is doing the platforming, no follow-the-sparkles.
I'd like more platforming that rewards exploration, and I'd like treasure to feel more rewarding again, i.e. hidden spells, summons and keychains. Outfits would be cool too. At the very least, accessories like bangles and earrings should appear visually on Sora's person.
I'd like the transition from gummi ship to world to be more seamless, and visually represented. I like the idea of a more nautical theme, with a sea of stars you steer a great gummi galleon over, with each world like bizarre islands on the horizon. I would love a full-on pirate KH, with a crew you gather up over different worlds.
I want Disney and Square villains to be a part of the story. There should be some kind of creepy trickster character, if not Kefka. I want Wonderland and Halloween Town back, and I want several fullsize original worlds. There should be a colosseum with FF characters, doesn't have to be Olympus. More RPG elements of choice, like Who do I take to the ball? and even multiple endings would be cool. I'd like Sora to get a reliable mentor figure, and maybe a pet.