benefit of the licensing proposal is that it will be easier
for Wikipedia and Citizendium to cross-fertilize each other.)
Nope. The "to clarify that attribution via reference to page histories
is acceptable if there are more than five authors." bit will mean that
it is imposable for wikipedia to take content from Citizendium without
Citizendium adopting some very strange TOS specifically for the
benefit of wikipedia which I would rather doubt it would do. Even that
would not make it possible to copy content on Citizendium to wikipedia
at the moment were the 5 names +URL proposal to be enacted.
I don't regard the 5 names+URL implementation proposal to be written
in stone. We might choose to modify it (by, e.g., increasing the
number of names, or allowing editors who insist on being listed to be
listed) based on feedback here and elsewhere. But the aspect of the
license update has always been to maximize the extent to which
Wikipedia can import and export CC-BY-SA-licensed content. Citizendium
uses a CC-BY-SA 3.0 (unported) license already. Presumably Citizendium
wants both to import and export CC-BY-SA content. Any implementation
by us that would require us to ask Citizendium for some kind of
exemption -- which I agree would be unlikely -- is out of the question.
Note that I used the word "easier," which is a comparative, rather
than "easy," which is an absolute.