Having had RRRE for a few months now, I'm really enjoying it, but there seems to be a few notable omissions from the GT3 class of cars, 3 manufacturers that I've noticed that are available in other sims but are missing from Raceroom, Lamborghini, Ferrari and Aston Martin, 3 cars that I really enjoy in ACC, I think that these would make great additions to RRRE, now I know they probably aren't in the game due to licensing issues, but those would really round out the GT3 class.
I should just do a search chap, this is a hot topic every now and again. If it's not in the GTR3 field by now, it's unlikely to arrive anytime soon™ and yes it's all down to licencing, they want too much bloody money more than likely but there could well be politics involved, usually is in some form or other. Believe the Mercedes EVO is incoming but Ferrari, Lambo and Aston are but a distant dream. I do also believe the new M4 may well beat a path to the GTR3 field in the future also, as well as a GTR4 version but other than that I'm afraid there is only disappointment heading your way regarding the high end marques you (and the bloody rest of us) wish for!