I'd have bought GTR3 for night and rain features. At least we got an update, and an apology I guess!!
There are 2 ideas I'd warm to. One, based on the concept of taking AC, Gran Turismo, and Forza, and build them with the quality/physics in UE, like ACC has. GT has road cars, and GT4 type variants. Forza has seen std road cars, which are modified generically into a racing car via tuning and parts. GT/Forza on PC, with more realism would be a hit I'd say. Just junk any unrealistic "VisionGT" cars, and have narrower tracks.
GT used real roads as a basis for the Tokyo location, and it looked and drove nicely. Cheaper than some real tracks, but importantly, variation too. I think SimBin could have announced anything licenced, and we'd have been happy. I think something like AC2, with a nod to Forza/GT would do well, if built well from the ground up. To do this, they'd need official licences for real data.
With a base sim, they could then sell DLC packs to cater for what "some" fans like. So, paid dlc for Hillclimb, rally stages, classic Grp A race packs etc., etc., could all be addons for a base game. Plus old Formula cars, and 60's racing beasts could be offered.
Second option - already pointed out by another member here. Let SBUK develop RRE2. Port RRE over to UE, let's finally have day, night, and weather. Announce RRE2, and offer it as early-access, once they have some base content converted. It'd be a great way to add more series' and life into RRE. Plus early-access would allow them funding to get a large team working as fast as possible. Those that are happy with RRE and are happy to dry lap, they don't have to buy-in. Let those that are unhappy with the state of RRE pay an early access fee, to help fund something workable.