This argument depends greatly on how much you're shortening copyright. Even if it went back to 30 years, I'm skeptical that it would impact it much. They may st

This argument depends greatly on how much you're shortening copyright. Even if it went back to 30 years, I'm skeptical that it would impact it much. They may still sell, but I doubt publishers are being kept afloat by works that old. Even for the IPs that remain popular they do new things with them to keep the revenue coming.