That's just how much grip is left on the tires, I know what your saying.
Shift 2 has a engine swap option, I dont think PD would know how to do it. They would be to busy making mx-5 at Tsukuba races.
This would give users the chance to be unique but most casual players would have no interest in this. When I mean everything, I mean, distributors, spark plug wires, timing chains, carbs, and all sorts of other stuff. All the way down to boring and stroking engines, even what brand of exhaust you have.
And this is my opinion of this...it's just too complex for the whole game to be covered.Remember, space is not infinite on a disc...