theres one class of car which is completly missing , the mid engine competition car, sort of a gtr version of the raceabout.
what i would like to see is a better mix of rally cars, lets have the equivelent of a mk11 escort, full on rally x mini, early quatro. all of these had strengths and faults and with a tarmac / loose mix none will have a dominant advantage.
oh yes there should also be a lancia stratos, which will please tristran, midengined rally car, very fast on tarmac if you could drive it, very twitchy on loose, once again no dominant advantage.
startos should be achievable as there are at least 2 "clones" available and one of them's pannels can actually be used as replacements on genuine article, so body shape and spec appears to be available or at least have a blind eye turned to it