Cait Sith's slots limit break would be pretty difficult to figure out how to get it to work, unless you would just have the various effects be their own specials. Getting it to be truly random would be pretty funny, though. Vincent's limit break would also be kind of cool to figure out what to do with. Have them all be one shot transformation/moves? Or have it like in the game where he's like that for the rest of the round and gets an entirely new but small moveset for each different limit.
I also think Barrett would be a cool character to mess around with, make him kind of like Gen from street fighter in that he gets a different moveset where one of his specials switches him between his long range weapons and his melee weapons. Make him a switchup character. although I should say I'm not suggesting we actually attempt any of this because it would be hard as a mothersmurfer, rather just thinking about what would be sweet in a proper FFVII 2D fighter.