I'd argue that once you've profited from it, that's a bright line that it's no longer purely yours to dispose of as you see fit.

I think an "easy" way to manage this would be to require people to submit a DRM free copy of any work they want copyright protections on to the United States Copyright Office who will keep a record of when copyright was applied, contact info for who to reach if you want to negotiate rights for using the work while copyright protections are in effect, a countdown timer showing how long until copyright expires, and once expired a download link for the work available to anyone at any time going forward.

It would mean that people's work wouldn't enjoy copyright protection (or at least not full protections) unless they give all that info to the copyright office, but I think that's a minor trade off for what would quickly become a vast repository of public domain works.