I could imagine more classes, but it seems like 4e already has all the core races it can hold, and then some. Wanna play a living plant? Done. Living rock? Check. What's next, living food? "My Donutborn Monk uses Powdered Sugar!"
Of course there are quite a few monstrous races still untapped, but most of us DM's would prefer that they didn't appear in a book titled 'Player's Handbook'.
PLAYER: I rolled up a Dragon Paladin!
DM: You mean a Dragonborn Paladin.
PLAYER: No, an actual ancient red dragon! He attacks the evil sorceress and does... 328 ongoing fire damage!
DM: Before we get to that, let's talk about how your dragon manages to fit into the Neverwinter sewer system.
If something like that popped up in a Player's Options: Monstrous Races book, though, I wouldn't feel as bound to allow it in my game.