Not quite accurate, there are major tell-tale signs that GT 6 is in fact a more robust package with features turned off than a completely native application. Even the reflective services from GT 4 are likely still there. Nearly every developer evolves their code base because at their core they are not that platform specific. It's why porting is so easy.
Currently GT 6 doesn't rely on any ps 3 proprietary tech like GT 5 did and any optimizations going forward will be pulling back on existing functions like we have seen on Bathurst.
As the current gen continues a slow decline, and next gen steadily increases, and boing GT won't be alone in the coming years, I'm pretty certain that nearly every future update will be in some way transferable to GT 7. For instance, we won't get new audio in GT 6, perhaps the tweet the existing system (frankly putting the exhaust note in the cockpit and bumper view would be a 100% improvement), and any new features or assets will transferable with the exception of one, the online clubs, but even that will be at least 50-70% reclaimable.
Just look at willow springs? Or any newer track. WS alone is so much better looking than any other track. They didn't even touch the Nurburgring so I bet that will get a major update for 7, but its clear the newer tracks don't just use better assets, but they are different assets.
Cars don't shine and have reflective surfaces in the dealer, but we know its there, just turned off, shadows on Bathurst's periphery are turned completely off, some tracks don't have pit crews but could easily be turned on, the LOD was pulled in significantly and is easy noticeable on Daytona's oval, sounds cut out, this isn't a bug as much as it is a safety measure to avoid overloading, AI is inconsistent at best likely due to a similar 'optimization'... Older photo mode locations are likely being prepped for GT 7, something you would assume is an easy drop it to GT 6, its clear zero effort went into career despite Kaz even agreeing GT 5 was too lean, physics, the core of the series and something that changes the entire foundation of a physics based game is clearly still being mucked around with, the list (or indicators) go on and on...
Digital foundry was spot on when they said its obvious to see when GT "turns on all the bells and whistles" how it will look next gen. Engine features we have all seen in some way in small degrees.
They will continue to use GT 6 as a bucket of sorts, like a safety build likely filled mostly with assets, while they already have a mostly filled up bucket for GT 7.
This doesn't mean GT 6 isn't worthy of a version, but its more clear now than ever before, that GT 6 is more of a step to GT 7 than any previous GT title has been, and they even admit it witch is surprising.
Also, pd didn't even market GT in the US (the largest and most vocal consumer market in the world), why? Because 7 is already well on its way and 1-2 years on on our watch is like 1-2 months on PD's.
Not only does it make perfect development sense, but it also makes perfect business sense and when those two are in alignment then it's already a reality.
If I admitted to you guys how many times I've done exactly what pd is doing and what titles, you would be shocked... And that's just me... Every franchise does it. Pd only focusing on one game doesn't follow the traditional 12-24 month dev cycles...