Seems Interplay isn't putting all of its eggs in the Project V13 Fallout MMO basket. They have another game in the works, although information is sketchy right now. From Chris Taylor:
We can't say anything until the game is publicly announced.
I think I'm allowed to tease and say that just yesterday I was told of a new game. But I can't say anything about it. ^_^
Cheers to Frymuchan for pointing it out!