Early Experimental Preview of Career Concept

I'm enjoying career mode alot but it lacks any incentive for building cars other than delivery one. Racing challanges supply you with car and using your own for them locks you from rewards and challanges don't lock you from using overpowered ones. They are good as "license tests" from GT series but that is kinda all to it. Maybe some kind of randomised event generator would fill that hole? Challanges that pop up in the world with randomised opponents in specific classes? Like FF, FR, 300hp, Turbocharged, Classics etc. Or maybe possibility to challange specific traffic cars for a race?