Here’s an idea:
According to Justice Breyer, in his dissent to the Eldred decision, only 2% of work copyrighted between 1923 and 1942 is currently being commercially exploited. That means the remaining 98%–books, music, movies, etc.–is commercially unavailable. Anyone who wants to use that work in any way must find the original copyright holder to first secure permissions before that material in any form. So if you run a film archive, and you want to restore and present a film from 1928, you must first find the current copyright holder. But what do you do if that copyright holder is dead, and his or her estate is unreachable?
Larry Lessig (yes, him again) offers a compromise: Require copyright holders to pay a small tax–Lessig suggest 50 bucks–to reregister a copyright 50 years after a work is published. The name and contact information of that copyright holder then goes on record. If the copyright holder fails to pay this tax for three consecutive years, the work enters the public domain.
This provides artists or musicians or filmmakers or writers an easy way to determine who holds copyright to a work and seek permission to exploit that work in some way. This also protects the 2% of work that is commercially exploitable, while allowing the other 98% to enter the public domain.