Though it's not a Gran Turismo title. Around the time of
Gran Turismo 3, it was said that after GT4, Polyphony would turn their attention to something else. An RPG was the
rumour. This plan is still on, apparently.
Polyphony have only released one prior non-GT title. That was Omega Boost for the PS1. An RPG by the company that
produced the Gran Turismo series is extremely appealing, if they keep the attention to detail they're noted for.
No further details at this point, so watch this space. Or a space just like it, anyway.
Engadget
TUAW