I can't see it ever happening, but a government forcing everyone to distribute the sources and rights to redistribute/modify along with their works pretty clearly abolishes intellectual property.
As a lesser thought: currently, when you publish a book in the US, you are legally required to send a copy to the Library of Congress. I could see the same thing working for software, requiring a submission of source code to some central publicly-accessible digital library. No licencing requirements beyond "people can read this," but that'd still be an unearthly boon to, say, security researchers.
