The original duration in the U.S. was 14 years, plus the option of a renewal for another 14. IMO we should move back to something close to that. One idea I’ve seen is that there’s an initial cost of however much for 7 years, and then the price doubles for every 7 year extension beyond that. Not even Disney can beat exponential growth, and it would force them to pick what they actually care about.
I’d also prefer explicit registration. We’re losing too many works because nobody’s sure who owns the copyright, and nobody knows if it’s safe to archive them.
I’d say that the original Star Wars trilogy should be public domain by now, for a concrete example. Disney can make new stories and characters in the universe and make money off of them, but everyone else should be able to as well.
Also as an aside, here’s Richard Stallman on why the term “intellectual property” shouldn’t be used. It’s an umbrella term that doesn’t really make sense, and more explicit terms like copyright or patents or trademark should be used.