Here is the villains that really need to be added as playable characters IMO
-Ridley, metroid needs a new rep, as well as a villian.
-K. Rool, DK needs a villian. also, I like him.
-Kamek, yoshi REALLY needs a new rep, and kamek is the only real option.
now, here are some that would be cool if added, but the game won't miss them if they aren't in.
-Medusa/Hades, neither have had enough games to determine the TRUE villian of the series. if another KI game is made, if one of the two was the villian, then that one would be more possible.
-Porky, a really liked-to-be-hated villian, but not promident enough in nintendo's all stars to gain a spot. if a mother series remake is indeed being made, he might have shot.
also, someone from fire emblem would be interesting, but I haven't played any games yet, so I wouldn't know what I would be talking about.