I wish the Imperial Army and Solar Auxilia could get more characters, but honestly I don't know what they could make aside from the named general and medic guy, because only those that stay in the back can survive and exceed against marines. Any sort of legendary peak human special ops unit would probably get wiped out in minutes by unnamed mook marines (like how the inquisitorial retinue of unique looking OCs in that one Dark Angels comic). I guess a named sniper or tank commander could be an option?