Full model replacements are typically not hard, especially if theyre being used as a replacment for already existing assets vs creating a new asset and item id for.
Its like the modding scene for both brawl and umvc3.
It only starts off with replacing already exiting assets, but it wont explode till you figure out how to add custom assets. Brawls point was when project m devs found how to add character slots, umvc3 was when they figured out similar + making fully custom models/animations without having to borrow existing ones.
You need the tools to exist to get to the blowup point.