By the way, that means that if authors are submitting
content to
Wikipedia, with the intention that nobody would be able to create a
derived work from their article and slap "all rights reserved" on it,
those authors are putting a lot of trust in the Free Software
Foundation, aren't they? Since the FSF might someday release a
version of the FDL which allows third parties to create derivative
works published under "all rights reserved", like CC-BY does. (Not
that the FSF is ever likely to do that, obviously, but it's still
unusual to have an agreement that one party can unilaterally change
at any time in the future.)
The license says:
"The Free Software Foundation may publish new, revised versions of the
GNU Free Documentation License from time to time. Such new versions
will be similar in spirit to the present version, but may differ in
detail to address new problems or concerns."
Removing the requirement that derived works be released under a free
license would not be "similar in spirit".