Very interesting points and reasoning... although I don't see how an earlier release of Gran Turismo in a console (thus having a smaller userbase) would hurt the IP. GT3 came out only 1 year after PS2's launch and it became the most successful game in the series. As the console sells, the game sells too. Is this hard to believe? In my opinion, the reason for the GT6 to have been launched on PS3 was because that was Poliphony's plan since the beginning. Like they ended a cycle with GT4 on the PS2, they wanted to do the same on the PS3. Plus, they didn't have yet any next-gen concept to deliver so, as you said, to launch GT6 (a game that only consolidates what GT5 attempted to do) on PS4 would have been strange at least.
As for the symbiotic relationship between Evolution Studios and Poliphony Digital, I don't know how real it is. What you said makes sense, these two can benefit from each other. But I'm not sure whether the shorter production cycles of GT games have anything to do with that. GT6 took only 3 years after the 5.5 years of GT5 and, like you, I expect GT7 to come after 2 years or so. But the reason for that I think it's not about cooperation with other devs. Japanese game studios have been realizing that controlled production cycles like the Western does (for example with Call Of Duty, Assassin's Creed and Forza) are much better for profits and even for the sake of the series than launching the game only when the initial ambition is achieved, not matter how long it takes (like it happened with Gran Turismo 5, Final Fantasy XIII, Tekken 6 and The Last Guardian that didn't even came out at all). Therefore, some of them are already adopting the Western good practices, including Square Enix (which launched FF XIII-2 after 2 years and Lightning Returns again after 2 years) and Poliphony (which is starting to shorten GT's development cycle).
Prediction made in 14/01/2014 for 31/12/2020: PS4: 100M XOne: 70M WiiU: 25M
Prediction made in 01/04/2016 for 31/12/2020: PS4: 100M XOne: 50M WiiU: 18M
Prediction made in 15/04/2017 for 31/12/2020: PS4: 90M XOne: 40M WiiU: 15M Switch: 20M
Prediction made in 24/03/2018 for 31/12/2020: PS4: 110M XOne: 50M WiiU: 14M Switch: 65M







