Well would they sell less well?
Also, the game has been out for 2 years now. Its growing in popularity. It would be going gangbusters if there wasnt a stock hickup at the release of wave 2.
Now there are a lot of people that are not playing the game. Granted not everyone has seen it being played and said thats cool, but if you regularly go to an LGS, and you havent made the plunge, then something is missing.
Will a new faction be that thing that gets people to commit? Maybe. Maybe not. But I cant see how it would hurt.