I disagree entirely in that I believe government shouldn’t determine this but rather the market. The rights to an intellectual property should be transferable/sold in perpetuity and at some point the work will become less and less valuable as newer works outcompete for attention. This will differ depending on how great the work was as judged by the market but it’s still the commanding force.

Any particular time for transfer from market control to public domain is arbitrary. If it’s worth anything it should be traceable not stolen. Everything will eventually have too little demand to be defensible and control will be let go and at that point it becomes public domain because it became public domain.