[Anm]

I also agree with purchasable extensions, as long as the prices increase exponentially from a very modest price in the first renewal.

Further, I think there is room to tie trademark into the process for media properties. In cases like Steamboat Willy, the character reflect a trademark for the Disney business. If it were applied as such, one might argue that a public domain version of the film (which could be seen as a product in the trademark domain) might be freely distributable but not modifiable without risking trademark infringement. This protects the free flow of information to later generations, as well as provides the company a means to protect the its brand from confusing or abusing variants/remixes. Further, registered trademarks already require regular renewal from a living person or operating business.

Not sure how one would apply that music and non-fiction (or if one should even try); seems about useful as copyrighting N seconds of silence.

(Obligatory: I am not a lawyer.)