I do like this idea, but T10 will definitely need some player data to decide how much “factory backing” would cost. I also think that Factory backing could be an unlockable feature for a manufacturer’s cars, provided maybe 1 (or 2) car(s) is leveled to 50 by the player from that same manufacturer. This is to prevent the car leveling system from being skipped altogether.
I also think that the Car XP system should be complimented by a “sponsor system” (which functions like the mod cards).