Mine would be different than what we have now, it'd be 20 years or artists lifetime, whichever is shorter - then 10 year long renewals are possible after that, but the cost of the renewal would ratchet up with each renewal.

I've also considered using a percentage of revenue for the work - basically a tax on the revenue from that work, as a condition for the right of monopoly on it - which would also ratchet upwards with each renewal.

I'd also consider a use it or lose it strategy for copyright like trademark, meaning if you are not making the work available for purchase/license within the copyright renewal period, for reasonable terms, you lose the ability to renew it.

Mine is mostly designed to deal with orphaned works, ensuring they enter public domain in a predictable way, I think the biggest issue with our existing copyright system isn't enriching Disney - they're still putting those works out there, making them available - its all the works being lost to the sands of time.