If only it were that simple, we probably won't be seeing the same amount of Premium cars as the total number of Standard cars currently included when GT6 is released.
To make a Standard car into a Premium car means remodelling it from scratch, or to put it simpler, they can't use the Standard car to create a new Premium model so they have to make roughly 6-800 new cars (depending on what's regarded as a fully different car) and each Premium car takes about 5-6 months to create.
So that won't happen for GT5, and I doubt it will happen for GT6.
Not so.
Provided the standard cars are accurate, it should be possible to use them as a low-res cage for a high-poly, current gen mesh. By no means would that make it a one-day affair, but getting a very accurate base mesh is a pain in the backside and can take a long, long time. That, and there'll be some form of unwrapping on them already, anyway.
I want McLaren MP4-26 Formula 1 Cars, actually more Formula Cars in general would be great. If they add McLaren, Red Bull, Sauber Mercedes, would be great. Although I could just buy the F1 game.
You have two options:
Buy the F1 game
Hope and pray to whatever god/s you believe will gave a toss, that PD will include a Formula Gran Turismo 2011 Edition. The old FGT was a ~2002 car visually and aerodynamically; the wings being a dead giveaway, but with a considerable lack of detailing around the sidepods showing it, too. A new Forumla GT could include a smaller, higher revving engine than the old 3.5L V12, wide front wing, narrow/tall rear wing, better performance on smaller, slower narrow tracks, and enough colours to make a grid look interesting.
The graphics from FM4 looks better that GT5 when it comes down to the auto vista feature. The racing gameplay will be quite the same but it will have improved texture quality and the brand new engine with the cars not increased polygon count like you see in the auto vista feature.
They're still undecided wether or not there will be a dlc. I would guess if they make lots of premium I'm sure they'll add some in GT5. If not we'll just see it in GT6. Does anybody believes that the Forza series will be the new king of all racers?
Actually, it appears they will be updating the car meshes this time for in-game - in F3 they only used the hi-poly models in the 3 second countdown before replacing the models themselves with F2 ones when you're in control of the car. The bad news is, if you couldn't tell the difference between the models before/after the countdown in F3, you won't be able to tell the difference between the old F3 in-game models and the new F4 in-game models.
Though, the biggest improvement seems to be the lighting and textures; they've got (or had, contracts have expired...I hear) some people who know what colour balance is, so even with the old models they look 10x better because the light behaves itself this time.