You could be right sure.
But there's a but:
The ingame cars are like 200k polys max, definately less than photomode models, so if they'll use photo-mode models as ingame models on the PS4, and upgrade them with new shader effects (texture resolution, lighting complexity etc.). This will make the cars look good enough I believe, no one should really complain by then I guess and would it really make sense for them to make EVEN more detailed cars? Which would take like 1-1.5 YEARS each for one person to model? I don't think so.
That's the problem... everyone focuses on polygons as if thats the only thing that will change...
GT4 cars were super high poly counts for the time (photo mode models especially) but guess what? No interiors modeled... that right there killed any kind of future proofing.
So the assumption that GT5's high poly cars make them future proof is flawed again becasue it focuses on just that one factor... what if the future allows for things like advanced damage model of an actual chasis and includes thickness and strengths of different materials? GT5 cars have none of that recorded.
What if advanced features like modeling actual weight distribution based on every part is used? What if damage actually skews weight in real time? GT5 cars do not have every part weighed, just overall car weight with possibly some overall weight distribution info.
How about undercarage wind resistance based on actual part shape? Not just cars that have a flat textured bottom...
And the assumption it would take so long to model is also just a guess... PD seems to do things the really hard way which takes a LONG time... but laser scanning has come along and who knows what techniques are coming down the pipes for the future? Plus pretty much every new car has really detailed computer modeled version from the factory already... that would save you a LOT of work.
See there is a reason almost nothing is ever future proof... you can't account for what might get invented in the future.
Graphics cards are never future proof no matter how fast the GPU because a new shader comes along or physix is the next big thing.
RAM is never future proof no matter how fast because a new architecture comes out... remember when DDR first came along?
4Ghz P4 processor? Oh look dual core...
8 USB ports, 2 Esata and 6 SATA ports? That's nice, does it have USB3?
Future proof is always a joke. GT5 cars are no more future proof because of their poly count than GT4 cars were.