I would be okay with just keeping it but limiting it severely. If you release music and you can't sell enough albums in 20 years, that's not societies problem. A lot of artists release albums every 1 - 3 years anyway, so they're always selling some records, or were before streaming became the way to "own" music. Most make their money off of concerts anyway.

For movies and shows, charge and increasing fee to renew the copyright. Eventually studios will give up certain movies. The older the movie the more you pay.