GT6 arrived with a wealth of new content along with numerous changes and improvements to the underlying technology - we're seeing state-of-the-art features that aren't even present in the next-gen Forza Motorsport 5.
there's a sense that GT6's assets were created very much with the future in mind: between the incredibly detailed premium car models, the advanced lighting solution, and the beautiful post-processing utilised in replays, it's fair to say that a boost to image quality and performance alone could make for a convincingly high-end PS4 title. Many of these details were necessarily curtailed by limitations of the PlayStation 3 hardware, but the systems that have been created here seem to be a great fit for its successor.
Gran Turismo 6 certainly suggests that Polyphony Digital has learned some valuable lessons in transitioning across generations this time out - creating assets at a quality higher than could be fully appreciated on PlayStation 3 certainly makes a strong case for this. The inclusion of features such as adaptive tessellation, which could become genuinely practical on PS4, only serves to further cement this position. By further refining the lighting, shadows, and track detail while increasing resolution and performance levels, we could be looking at a proper PlayStation 4 sequel.