Provided that we go back to the original term of copyright, 14 years with a 14 year extension.
Everything up through 1980 should now be in the public domain.
There is an interesting idea of basing copyright law on the original General Mining Act of 1872. It was simple in concept, that anyone could stake a claim anywhere, but it either had to be “improved” by $500 (1872 money!), or had to provide $500 worth of ore each and every year, or the claim became invalid.
The way this would work with copyright law is to say that anyone can copyright their work, but to get government protection for that work, but after 10 years, they must retail that work for a given profit every year, or lose their protection.
This is extremely pro-marketplace, because right now there are copyright libraries of immense size that are not sold, just archived, yet have government protection against anyone else selling them.
So a creative person has two choices. They may either keep their work private, or they may sell it until nobody else wants to buy it, and then it loses its government protection.
Look at the Walt Disney Corporation for example. The character Mickey Mouse is worth a retail fortune to them every year, so they could easily retain copyright over it. However, while they have the copyright to the movie Song of the South, they both refuse to retail that movie or allow anyone else to retail it.
This latter action is anti-marketplace, so while they have the right to not retail it, they do not have the right to maintain government protection to not retail it.
The way this new copyright law would be set up, new works would be protected for 10 years for free, giving them time to “find an audience” with copyright. However, beyond that, they must retail their work or lose the privilege of protection, so others may try.
The huge stimulus to the market would be tangible, as much of these vast libraries would not be able to make the minimum retail demanded of their copyright. So if anyone else had a copy, it would in effect be public domain.