20 to 30 years would ensure that abandoned media that was formative to a person growing up will enter the public domain within their lifetimes which would be a nice thing to have in my opinion. It would also ensure that any work done by an artist during the early phase of their career (the phase where artists are most likely to agree to lopsided contract terms) would stand a chance of reverting back to the public domain before the end of that artist's career. Very very few works are making any significant revenue after 30 years. I think a system where initial copyright is free for 20 years, with the option of renewing for an additional 10 years for some fee, and then the option to renew annually after that would be fair. For the very small number of works that are still commercially viable after 30 years, the publishers can figure out how long it makes sense to keep renewing the copyright. Otherwise it really is in the public's best interest to have a robust public domain. Many fewer works would go missing that way.

The way the copyright is structured right now is the result of regulatory capture. The cost of these long terms of copyright is the loss of books, movies, music, games, etc. Millions upon millions of hours of creative labor have been lost. These costs are born by everybody that will never have to chance to have access to that media. The benefits of these long copyright terms are only the publishers. Having an annual renewal fee for copyrighted works published 30 or more years ago would be something that would be a visible cost in the books of large publishers. As it is it is too easy for them to ignore the downsides of long terms of copyright. I am not claiming that no media would be lost if we had no copyright, but the efforts of archivists are difficult enough as it is. Media that is no longer being copied is destroyed eventually. Obviously making it a felony to copy something will reduce the number of people making copies of it. That's the whole point after all.