Soon after PlayStation 4 was announced, a Sony exec accidentally outed Gran Turismo 6. Curiously, he referred to it as a PS3 game, not a launch title for Sony's upcoming console. New retail listings also refer to GT6 as a PS3 game, suggesting the loose-lipped exec was probably telling the truth.
Given GT5's lengthy development, it wouldn't be surprising that Sony would want to push out one more current-gen iteration of the franchise. PS4 owners, on the other hand, may be interested in that platform's go-to driving simulator, DriveClub.