The big question I have at the moment is weather there will be anymore newcomers, specifically if Rayman will be playable or are 66 characters too much for the switch to handle?
Tech specs aren't what the determine the max number of fighters, just how many fighters Sakurai and his team can push out before the total number becomes too much for a fighting game roster.
Gameplay wise 65 as is already alot especially considering some of that is already bloat. They might reveal a new character or two maybe.
They'll definitely be revealing the rest of the stages and modes, people been brown townyzing the current stuff we've been given and so far we know there's 70-80+ stages in the game at that point I wouldn't be surprised if every stage was in.