Knowing Polyphony's penchant for Japanese automobiles, why not a Mitsubishi Galant Lambda? Of which was sold in Australia as the Scorpion, and the US as the Dodge Challenger/Plymouth Sapporo.
Or how about the 1st Gen Eclipse, which AFAIK has never been seen in a GT game?
Finally for the 3 Diamonds, a car that this site rumored to be coming at some point back in 2018, but hasn't appeared thus far, the Mitsubishi Starion? We've had the Rally version before, but no road going counterpart. I feel these 3 cars would provide much needed diversity to the currently Evo heavily lineup.
Pivoting to non-Japanese cars, GT has never had a Fox-Body, and while many would opt for the 5.0 GT, with PD's knack for the eccentric, the 1986 Turbo-4 SVO Mustang would be a cool add.
And continuing with the Ford theme, a car that I think is unlikely considering PD's lack of history with American Personal Luxury Coupes, but would be cool to see, the 1987/1988 Aero Thunderbird, either V8 or the Turbo Coupe would do.
Or Maybe the 'Bird's rival in the Bowtie brigade, the Monte Carlo SS?
We've had the Solstice concept, but why not the production spec version, maybe in GXP trim?
Considering Skoda is in the game as a brand, currently standing with only a VGT car to it's name, the Porsche of the east would be an interesting odd ball addition. May only have all of 58/62 hp on tap depending on version, but as they say, it's more fun to drive a slow car fast than a fast car slow. And think of the engine swap potential..... Maybe drop the engine in from the 83 Golf GTI?
Continuing the seeming theme of 80's cars of interest, how about the return of a brand absent since GT6? Can't go wrong with an Opel Manta(especially if PD adds a cheeky fox-tail as an extra accessory
)
Rolling back the clock to some earlier European GM muscle, the Vauxhall Firenza HPF would bring back the British half of the duo. Though this and the Manta's inclusion might be hampered depending on Stelantis, and how they treat the GM part of the brands heritage.
MG isn't a part of GT's make roster as of now, but as a pipe dream a ZT would be awesome to see
Modern Front Engine Ferrari's don't seem to be well represented in the GT7 car list, and the 550 maranello would help change that.
I know many people want the Audi V8 quattro to complete the 80's/90's DTM roster, and I'd be lying if I didn't agree.
A more modern car for a brand that could deperately use some lineup variety, the Hundai Elantra N
Add in the i30 N and you now have a respectable lineup.
And finally, a Mercedes addition that would be cool to see is the 560 SEC, a mighty and muscular V8 powered Executive Grand Tourer, that even has an even beefier AMG version should PD so choose.
Those are just some of the cars I'd like to see in GT7(or GT8 whenever it comes out)