Here is the full resolution image from Kaz's twitter:
Doesn't help me but might give some clues to the better guessers.
Heh, my turn now!
1. Mitsubishi Lancer Evolution VI GSR TME SCP '99, my second guess is the Lancer Evolution IV GSR. The headlights and hood match those cars too well. It can't be an Evolution VII as the headlights are too thin here to be anything newer than a 6. For the VII to IX, the grill would have to be wider aswell. Very good either way, Mitsubishi needed some more cars.
2. Most definitely what others have said, the Nissan R92CP Group C race car featured in GT4/5/6 as a standard car, now at last remodeled. It was a matter of time before that got premium treatment that the other Gr.C cars received in the past.
3. It's clearly the prototype Lamborghini Miura P400 Bertone featured in GT5 & 6. It makes sense as PD wouldn't have to do as much work to implement that in GT Sport as making a new model. I mean granted, they could tweak the model to be a regular, Miura S. I think that's unlikely however.
4. At first, I couldn't decipher what car this was, I knew it was a supercar or something. However, I can safely say that it's the Sauber Mercedes C9 race car. It was already a premium in GT6, so PD would just have to update the model to be PS4 Pro ready.
5. Yeah, obviously the Fiat 500F '65. I hope people replicate the RMs of it from GT2.
6. It looks like a Renault Megane, the fenders and front bumper lead me to think it's the Trophy Race Car featured in GT6.
7. The front end at first made me think of the Renault Clio, but the taillights looked more like a Ford Fiesta. Now though, I would say it's a Toyota Vitz, probably the Grmn version. I guess PD isn't done with adding Toyotas, heh.
8. They're definately not done, because that looks to me like another 86. Either that or a Subaru BRZ, I'm hoping for the facelifted 86. Otherwise, it's getting a bit redundant. Then again, PD has been known for that in the past.
9. I'm going with what others have said, that's a Jaguar XJR-9 Race Car. It was another premium in GT6 that would be easier to retouch for GTS rather than making a new car model. This would make possibly 3 Group C race cars for this months update, similar to the 3 Super GT cars added for March's update.