I voted 7m, but this is pretty much impossible to guess. The near future is filled with strong PSP releases in Japan. As long as that continues, numbers for the Vita are going to be low. If they got those types of games on the Vita, however, we'd see a boost. I also have no idea if Soul Sacrifice is going to push hardware or not, either.
TGS is going to be very important for the Vita one way or another. E3 might be, as well, if they have another Assassin's Creed: Liberation level game. I really have no idea what the end of the year is going to be like.