How about we don't have an underwater music level period? We already saw how horrible that worked out in Kingdom Hearts II.
I don't remember hating it, it was just a silly mini game and it was over pretty quickly, maybe I should play KH2 again. It could work, I love Theatrhythm Final Fantasy, so I'm open to music mini games, they could do something similar but with Nintendo music I guess.
I'm actually serious about this, I think I'd enjoy it.