Saints Row? They originally wanted to make a Saints Row game for the 3DS. The canned the 3DS version stating that they were bringing it to the Vita. By the Vita's release date it flew under the radar.
It's going to be GTA 5. There has always been a version of GTA (more than one) on the psp. I'm nearly 100% it will be GTA 5 and when they do announce it the first thing I'll do is jizz my pants and then pre-order it. L.A Noire wasn't that great so I assume it wont be it.
Gran Turismo would be good, but it would take another 5 years to be released after it is announced. GT PSP took forever. Polyphony Digital is a joke. They take forever and then release half ass products like GT5.