Sure, but a manufacturer couldn't sell a car with a solid steel bumper. In the US you have lots of freedom to modify your car after you buy it, but manufacturers have strict regulations.
An interesting point: the oneupmanship game of aftermarket car customization will be the worst deficiency this thing has in terms of appealing to what I presume must be the target audience. Perhaps a radically modular interior could partially make up for the lack of exhaust systems etc to replace with custom counterparts? (the "back to the future air intakes" joke will get old very fast)
