Spring Man, Sukapon, and Ashley. Probably won't be the most popular picks, but they would all bring something interesting to the roster.
Badge Arcade Bunny would also have been a cool out-there pick a la Wii Fit Trainer. Lyn and Krystal both would have been great picks around the time of Brawl but I think their opportunity to be playable has probably passed.
EDIT: Shit I forgot about Bomberman! He's maybe the most glaring one along with Spring Man, but I'll stick with my original picks just because I want Sukapon and Ashley to get some votes.
Badge Arcade Bunny would also have been a cool out-there pick a la Wii Fit Trainer. Lyn and Krystal both would have been great picks around the time of Brawl but I think their opportunity to be playable has probably passed.
EDIT: Shit I forgot about Bomberman! He's maybe the most glaring one along with Spring Man, but I'll stick with my original picks just because I want Sukapon and Ashley to get some votes.