Upon further though, I do think that a potential return of the RM mechanic should be reserved for non-grouped race cars, like those based on the aforementioned Mazda Roadster (NA) and the Honda Civic Type R (EK), if only to keep the prices relatively unified. That said, I think this could be a great way for some of the touring car/RM models from the PS3 era to return, like the those based on the third-gen Prius and the CR-Z.
Now, as far as venues that could really use rain, I don't know if I'm missing anything other than Daytona, Watkins Glen, Brands Hatch, Trial Mountain, Tokyo Expressway South, and Interlagos.
I'd say Daytona, Brands Hatch, and Interlagos could especially use it, considering their respective locations, but at the same time, I think it had just rained quite a bit at this year's IMSA round at Watkins Glen, didn't it?