While I agree Ridley would be most fitting as a boss, I really don't see the logic behind this whole "he's too big to be playable" rationale. First off - Giga Bowswer. Okay, not really, but still - all they'd have to do is resize him; almost the entire Smash cast is not scaled accurately given the differences in character size and artistic/stylisitc proportions. Samus, Captain Falcon, the Zelda cast and the FE guys are all about normal human size and proportion, but Mario and Ness are not (smaller bodies, bigger heads) and then you have guys like Kirby, Sonic and Mewtwo who are supposed to be something like eight inches, three feet and six feet tall respectively. Obviously the heights and proportions are retooled as necessary, so there's no reason they couldn't do the same for any character.