^^^
But if I was totally honest with you, If we're looking at older Disney movies, I can think of like two and one of them isn't a full length movie and like to see some Cameos.
So for older Disney movie Worlds
Jungle Book : That fact this movie hasn't made an appearance is so shocking to me. JB is very priotrize if we're looking at older movies since its getting another Live Action movie by Disney "Jungle Book 2". Plus those UX medals, I mean we have to get at some point and looking at the graphics of Today Jungle Book would be beautiful.
The Legend of Sleepy Hollow: This is 1949 old! But it has one of the most intimidating Disney Characters. The Headless Horseman would fit so well in this damn franchise! You don't need even need Ichabod, The HH is practically a Heartless through and through, He can be a Disney Character you have to fight multiple times, and I think the first time you fight him is in The Sleepy Hollow world. But it be cooler if can chase you down through multiple worlds maybe another Disney Villain or the next KH Big Bad has his head or something, but other than he has some reason to chase you. He can be a very dramatic Boss fight since he is almost like Chernabog.
For Cameos: Kind of like Merlin
Marie from the Aristocats: If you didn't know this character is very popular in Japan. Maybe there is a mission where you have to save Marie from a group of Heartless in Twilight Town. It be a cute a cameo to another old Disney movie that isn't too well known.
I'm not sure if they'll get a world or not, But I would like to see the characters from The Emperor's New Groove just walking around in Twilight Town or something. It be another awesome cameo to a movie that has quite following (mostly from memes). Kuzco, Pacha, His Wife and his kids. Maybe there can be a minigame with them, who knows!
I just wish we had the power to Tell Nomura these ideas for KH4, Maybe tweeting to the Japanese Kingdom Hearts site could get their attention, who knows.