With a system like the Wii U on the horizon, I wouldn't be surprised to see developers making games for both systems down the road. Unfortunately, integration of the the PS Vita as a controller likely won't be implemented until after the launch of the Wii U.
Yes, I thought of that too. I don't see sony actually making any Wii U type games for the PS3/Vita. Maybe one or two. The market would be too small. However, just making the PS Vita a controller couldn't be that much work. They already have PS remote play which allows people to play games like Red Dead Redemption and other big PS3 games. It is a couple steps away from being a controller.