Yeah, I really want those as alternate costumes.
I also really hope that the E3 trailer shows alternate costumes so I don't end up feel like an idiot for being so sure they'll introduce actual alternate costumes this time.
... it'd be so easy for the game-makers to implement, the only reason I think they might not do it is if they can't think of alts for some characters so they decide to nix the whole idea since it'd seem unfair to those funny-shaped characters.
Edit: "Those" in this case means Dry Bowser and Meta Ridley, not the other devilry that's going on in this thread.