Matthew Britton writes:
Allowing people to "opt out" like this simply isn't possible.
I think it's only theoretically impossible. As a practical matter, I don't think it's much of a problem. I believe we could work with the minority of contributors who believe their content cannot be migrated in a way that is satisfactory to them.
I imagine most people who have been contributing for any length of time share my view that our contributions are effectively public domain and, regardless of what I, the Foundation or indeed anyone else does, have been and will be used in many different ways without the slightest bit of respect for the GFDL or any other license.
This is in fact what makes it possible, as a practical matter, to accommodate those contributors who object -- most contributors aren't personally invested in the specifics of the GFDL.
As Andrew Whitworth writes:
Besides a few GFDL ideologists, most contributors wouldn't care at all if we switched licenses, and many would welcome the freedom of a less restrictive licensing scheme.
Now, I don't disagree with Tim Bartel's point that:
Clauses like '...or later versions.' are invalid in German jurisdiction and only the rest of the license applies. [Delphine makes the same point about French law.]
... but I think as a practical matter this is not a problem, because you'd have to find a copyright-holding Wikipedian in Germany who (a) doesn't want to relicense, and (b) would prefer to spend money on litigation rather than simply withdraw his or her contributions (from Wikipedia, not from any other venue that is using the content consistent with older GFDL versions) . And even if you could find someone for whom both (a) and (b) are true, the fact that WMF would likely withdraw the contributions anyway if litigation were even hinted at would go a long way towards building a legal defense for WMF in such a case.
--Mike