Agreed. I see no reason not to make the small changes so that the standard "duplicates" of cars can all become premium. It certainly seems like not much work to me so why not?
Of course that won't stop people from saying:
"Too many japanese cars like usual!"
"bah stop making 1000 skylines/s2000/nsx/rx-7/miatas!!!"
I have no problem with duplicates as long as there is a good reason to include the alternate/newer/older model, just as it was in GT4. It doesn't take a genius that you could probably make 20 duplicates of one car before it takes anywhere near as long as making a seperate premium model of another car entirely.
Anyhow, apart from duplicates being the obvious choice, I'd like to see (in order of importance);
1.
Strange omissions Supra RZ, Veyron etc.
2.
Exotics, XJ220, Countach, S7, C12 7.3, ZZ-II, Furai etc.
3.
Race Cars, Minolta, 7, 2J, 2D, F1 GTR, Speed 8, GT One, FGT etc.
4.
Classics, self explanatory
5.
Unique/rare cars, Hommell, ZZ-S, Garaiya etc.
6.
Common Domestics, self explanatory
EDIT: Okay from the famitsu interview
http://www.andriasang.com/e/blog/2010/12/15/gt5_plans/
Famitsu also asked if plans are in place to redo the game's low fidelity "standard car" models as higher quality "premium car" models. Yamauchi responded in the affirmative. "Among the standard cars are some historical classics, and we plan on remaking them as premium cars. There are currently some cars that have both standard and premium versions. Those are cases where the cars were remade."
So it looks like historical classics will get priority. I'm cool with that. No idea if anything is ment by the "some models have standard and premium versions..." or if he is just stating the reason. I'd like to hope they are considering re-doing many of these simply because of the ease of it, of course as I said above that could create backlash from people who only see "WHAAT THEY MADE MOAR SKYLINES PREMIUM! I HATE YOUS GAIS!!!".