Well the KH3 Ultimania has released in Japan.
Apparently there wasn't room for Final Fantasy characters in the game for the same reason they weren't in BBS's Radiant Garden. Large amount of characters in the main story. But they did have a polygon model for Leon made.
Lol what? That cracks me up
Most of the characters that needed saving didn't show up until the end. And they barely focused on Lea and Kairi. You could have squeezed a scene or two of Leon and possibly the others