I'm pretty sure it made it's debut on the Grizedale Stages in 2013/14??? can't remember now, whether Matt or Elfyn drove it; I did film it on my old i-Phone.
However, I certainly think R5+ but with a 'spec'/ control hybrid could work. I also think that everybody has to be pragmatic (FiA, Manufacturers, the Promoter, etc), whilst trying to keep the sport relevant to those same Manufacturers.