Formula RR will be the fore runner for 4 open wheel classes which is 3 more than F1, so will Codemasters compete in 2016? (hope not as not impressed at all) hopefully with the historic open wheeler being one the doors will open for some historic LeMan type cars, 312b and 917 etc Off topic but went off track in the TT earlier and when I returned to track I swear Anthony has sampled a tumble drier drying jeans with a belt still on for the dirty tyre sounds!
But if implemented well, it would most likely be a big deal, no matter if it is just couple of cars and a track. At the least, it would most likely require huge rewrite of physics code as gravel stuff including tire models is pretty different from asphalt. Gravel racing most likely hasn't been even the slightest design factor so far during the developement, so there would inevitably be a lot of work to do. There is still so much work to do with R3E, so the last thing I'd like for them to do at this point is to deviate from their current design and use resources to some new novelty project within the R3E. I also prefer that S3S would keep their focus on what they do best: historic and modern GT racing. I don't still necessarily find open wheelers that bad, they can certainly bring new people in.
Being such a small team I wish S3 would just focus on GT and Touring cars plus tracks. As has been pointed out Rally and F1 has been covered extremely well already.
Formula cars make sense because they are on pavement like the current available cars. Rally would require a ton of work for off-road handling, hence the backlash from folks (like myself) who are waiting on tons of other features to complete the base game.