I have always maintained that Wikipedia editors should be implicitly appointing WMF as their non-exclusive agent whenever they edit.
That's as may be, but the fact of the matter is that the WMF is *not* a non-exclusive agent. In fact, the WMF didn't even exist when many of the edits were made. It is far too late to change the way copyright of Wikipedia content works. It is released under the GDFL and only the GDFL and will only ever be released under the GDFL. Accept it.