The linked FSF statement by Eben Moglen is about enforceability, not future GPL licenses. The normal state of affairs for a GPL'ed project is having mixed copy

The linked FSF statement by Eben Moglen is about enforceability, not future GPL licenses. The normal state of affairs for a GPL'ed project is having mixed copyright. After all, you can't stop anyone from forking to add their own, copyrighted, changes. That's the whole point. If mixed copyright means the GPL doesn't well enough, then the GPL doesn't work well enough, period. This is not an anti-GPL statement, on the contrary: Most people seem to trust the GPL well enough to not require copyright assignment. The FSF is the odd one out.