Requirement
would be to give credit via the credit URL, and by mentioning
the principal authors listed at that URL. What authors will be listed at
that URL is something that we may change at our leisure: for example,
this may be the proposed list of five authors, or none if more than five;
or it may be a list of authors that is no longer than 1% of the length of
the article, or none of longer; or, when appropriate software is
developed, the list of principal authors as recognised by the software;
it may even differ from project to project, for example Wikisource may
choose to credit the authors manually (it is already doing something
similar); and so on and so forth.
Any system other than crediting everyone or crediting no one requires
choosing people. How do you propose that to be done? And why doesn't
the person that contributed the 6th most text (say) not deserve to be
credited for their work?
I don't agree with that; I do believe that every author with significant
(copyrightable) contribution should be credited.