Georgism [1] but applied to copyright: If you want to extend your copyright past, say, 15 or 20 years, then you need to estimate the value of that copyright and pay tax on it. You can name any value you want, but someone can then buy it at that value.
Maybe there can be different rules for copyrights owned by humans vs corporations; 5 years free for corporations, 20 years free for humans. Or maybe longer for humans, I dunno. But having corporations sit on IP just because they can is ridiculous.