There should be some kind of "challenge" process where people can demand that rightsholders "put up or shut up", or lose their work to the public domain. Right now, we have a perverse incentive where publishers are incentivized to say they DO NOT own a work, in hopes that someone will do all the work of making some derivative work and then they can swoop in and demand rent. There should be a way to say "we asked for proof, they didn't respond, so our ass is covered here, go pound rocks, Warner Brothers, Activision, and/or 20th Century Fox".

Obviously this would only apply to things that sold above a certain number of units, making it something of cultural relevance. We also don't want this law abused to steal things if someone gets a copy of your dropbox files and you can't afford a lawyer to respond to legal demands.