I was surfing the net yesterday, as you do, when I noticed a strange IGN article from 2004. In it, a supposed GT4 Portable was releasing in 2005... Then we waited four years and got the half-baked, slow to play and bland GTPSP. Why oh why could they not add a GT Mode to GT PSP at least! Wanting GTVita please Poly...
It wouldn't surprise me if there had been a GTVita in the making (very early) and then cut after seeing how poorly the Vita sold outside of Japan.