[..]

Actually, an author can guarantee that they are in a position to assign the copyright to the document to the XSF. By, literally, saying so.

This indemnifies the XSF entirely (as long as we ensure it's explicit, which I believe we do) - as far as the XSF is concerned, we had the copyright assigned to us by someone who warranted that they were able to do so. Therefore, we believe we own the copyright in good faith.

[..]  I would first and foremost suggest that AI generated text is just one aspect of copyrightability and copyright ownership, and concentrate on whether or not the submitter asserts they have the right to assign, and have done so.

I agree with this point of view. It does not matter how the work was authored or by what or whom. Making a special case for AI does not make sense to me here, and may actually make it harder on the XSF.

 [..] I would much rather require that assignment (and the corresponding assertion of ability) is made much broader, and covered for example this message, and messages, comments, and so on in other XSF venues.