What do car companies do with the designs of older model cars. I imagne that a car company could get extra money for licensing a design for a popular older car. I also imagine that for a car company that doesn't have a large R&D budget this would be a cheap way to get a good design for a car.
I actually think that this is happening already. Take a look at the 1999 Isuzu Oasis and the 1995 Honda Odyssey.