Without the Porsche license, my preferences are limited a bit, but I'd love Capris v CSLs v Opel Commadors from 1973, ideally with Escorts v 2002s v Alfa GTAms as a secondary class.
If Porsche license was available, the early DRM years would be suitably fantastic, such as 1977 with Escorts and 935s supplementing the 320s we already have.
I'm not such a fan of the 80s and certainly not a fan of Super Touring (although I loved it at the time, I don't think they've aged well), although I wouldn't complain if we saw the Jaguars and Rovers (maybe just a TWR licence!) to add to the 6 Series and Volvo 240s.
Other than that, I'm a big fan of the modern series approach and would love to see the Blancpain Endurance/Sprint licenses realised in R3E.