Sure Joachim looks out of place, since he is just a boss.....unless they have put in him a story, like how he went to fight Walter and got imprisoned, like the sisters mode from PoR. Maxim you just could say that you've played his side, before he was consumed by the Draculas relics power and the Juste story never happened since it was prevented by Maxim, i don't know, i just like to play from the side of some other character the game, but if he doesn't have a story or at least something interesting to offer, then being or not being there is pretty much the same to me.
Alternate costumes is an interesting idea, but not with silly designs. They could offer you even some kind of new power, but that is for those who like stuff like that i guess.
Characters from CV3, they didn't required something special to unlock them, they depend on which path you'll chose and beating the area boss, so they weren't something special, they were meant to be playable from start of the game to the end of the game.