I agree that it is an interesting solution for teasers, possibly no return rentals. From a consumer perspective, no one would buy a disk that would be useless after a few days (DIVX?). And, if it was pushed on the public, people would just rip the content within the visible time.

I am thinking more from the novelty perspective, and the "how is it done" reverse engineering. The polycarbonate must be either light or moisture sensitive, becoming opaque after a certain amound of exposure time. A coating? Could it be polished off? That kind of thing.