They posted some clues for the November DLC:
Car 1 Clue 1
I have seen nearly as many wishful thinking guesses for this car as I did for the C6 Corvette and the 2015 Mustang. But this is far from similar to these American beasts.
Car 2 Clue 1
Mmmm, this car is a breakout from its brethren models, but forges a brave new path.
Car 3 Clue 1
The Smoking Tire, smoked some serious tires in this ride.
Car 4 Clue 1
Jumpin' Jehoshaphat, this little brother is worthy Don Johnson's approval.
Car 5 Clue 1
Is it European or classic JDM? You wouldn't know unless you know.
Car 6 Clue 1
Even Johniwanna knows that this car set a new level of expectations in rally and in production.
I am almost positive that Car 3 is the Jaguar XF-RS because of
THIS.