A Mr. Mime evolution would be interesting, though how Gamefreak would achieve that is unknown, because they would have to make a play on his name somehow, which I imagine is pretty difficult to do. XD;
Buuut....and this is just me...if any Pokemon could have an evolution, it'd be Ledian. I mean, it learns three of the most amazing moves that a Pokemon could learn in competitive battling: Reflect, Light Screen, and Swords Dance, and yet it could use none of those because 1. Stealth rock weak and 2. It's weak to like everything.
So yeah, I'd like the poor cute ladybug to at least get some recognition. D: