I expect that the cost would outgrow the financial reward of retooling a factory to make an exterior using materials and processes that are no longer industry standard. I also believe that they also license out this kind of niche manufacturing to other companies. I know that the Ford GT body and parts were licensed to another company so that they could keep building them for interested buyers after Ford ended their limited run.
Thats a good point, but I was thinking less of a niche product and more along the lines of why (to keep using Ford for an example) they don't just announce that the next generation of Mustang is going to look exactly like (to keep using my prior example) the beloved 64 Mustang.
