>Lastly, a GPL license wouldn't be possible to enforce without copyright, or the concept of a copyright owner.
Yes for the GPL, no for copyleft. The GPL was simply a mechanism that Stallman et all found to enable copyleft without having the power to rewrite the law.
If you did have the power to rewrite the law - and if you were to eliminate copyright, you would - it'd be perfectly possible to add a 'copyleft right' without relying on copyright.
The problem is that in Common law all those rights are based to the Copyright concept, and that blinds people to assume that must be. Here in Europe, we have 'authorship rights' - such as attribution - and they are not based on copyright; copyright is just one of them. You could take it out without affecting other authorship rights.