This is an aside but I wonder how a system that expired copyright based on sales and time would work out. Like copyright on a book expires in 10 years or $100,0

This is an aside but I wonder how a system that expired copyright based on sales and time would work out. Like copyright on a book expires in 10 years or $100,000 in sales, whichever is first. If the public loves the work so much that it exceeds some arbitrary sales threshold, then it must be of some importance in the popular culture and should be shared more widely.