In regards to drive forms we are still missing the third Magic and Guardian form. Merlin is in the game so we could get the third magic form keyblade from him. Guardian I'm not so sure unless we get another Disney cameo like Remy
Completing all the minigames for the Classic Kingdom would most likely give us our final guard form, a Keyblade reminiscent of monochrome from Timeless River would make sense seeing as Classic Kingdom is a tribute to Mickey Mouse shorts.