I think this is a good idea, though some of the older cars will need more than just shader work.
Now, I know that listing every car ever will not help things but I am going to list some of the ones I had some fun with or were memorable in some way or another.
Normally I would attempt to do it myself, and fixing up a shader file is doable but getting the audio right can be an issue and properly setting up the suspension is beyond my capability atm.
****
name=Plymouth Barracuda
year=1968
credits=Ryan T
comments=Formula S - 340cid V8
id=cuda340s
****
name=Plymouth Hemi 'Cuda (Alpine White)
year=1970
credits=Sven Franic, ini by: Mr. Whippy 2003.
comments=v. 1.0
id=alpwht
****
name=Plymouth RoadRunner (vitamin C orange)
year=1970
credits=Mesh and textures by Shmelby; ini,sounds,shaders by Alex Forbin
comments= For Racer V0.5.2Beta4.1
id=rr4406
****
name=Nissan Skyline HT2000 GT-R
year=1971
credits=Model by Endo, ini by Endo (based on ini by Cosmo)
comments=BETA TEST VERSION
id=KPGC10_v0011
****
name=Chevrolet Camaro Z28 5.0 V8
year=1984
credits=Car by Bumper - INI by CUL8R - All credits in readme.txt
comments='Tuned Port Injection' 'V 1.0'
id=84z28
****
name=Ferrari 308 QV
year=1984
credits=Car by f50. ini tuned by Mr.Whippy
comments=Euro version of the Classic F-Car.
id=308qv
****
name=Toyota Sprinter Trueno Advan Kurata
year=1987 v1.2
credits=Model by Endo, ini by Cosmo°
comments=Cup Car
id=AE86_lite_v1001
****
*Edit
That 68 Barracuda still looks pretty good considering it's age(cept for that odd block in the centre of the dash), was a very fun car to slide around Schuchter.
The Hemi 'Cuda, need I say more?
Same goes for the 70 RoadRunner (yes, I know there is a 71 as well but I did not end up using that much so it did not make the list even though it is still cool) The model of this one last I recall, like the 68 Barracuda did not age too badly.
The KPGC10, it may not be insanely quick but like the 68 Barracuda was fun to take out on Schuchter among many other tracks, actually, Schuchter should be updated too!
84 Camaro, I like thirdgen f-bodies so this is a must. If the model has aged too badly, one might perhaps try slipping the forza camaro or firebird in and having some private fun like that. I *do* seem to recall this car flipping over more frequently than it's real version should..(at least I think that was this car) it most likely needs it's suspension&tires looked at closely.
Ferrari 308 QV, I seem to recall that this one has a set of keys that sway back and forth, I loved that extra touch! I also seem to recall that the model has aged fairly well, though I have not really used it in a while. I think this is perhaps the only Ferrari I have seen that I might want to own irl if I based my purchase on looks and had lots of money.
The AE86 is quite a hyped up car sometimes, and normally I avoid the "FnF ZOMG DRIFT CAAUR" thing, but it is a neat little hatch that I think deserves continued use. It is also not designed in the 90s, so it gains points there as well.