User blog comment:Kirkburn/Technical Update: September 2, 2015/@comment-1757994-20150903225322/@comment-1757994-20150904003217

It's deflection. The lack of ability of one user to edit another user's js is irrelevant to whether users can edit their own js. Users have always lacked the ability to edit the js of others (unless they had edituerjs because they were admins).

So the real answer is: you don't know. Well, then I guess I'll look forward to whatever the answer is a few months from now.

As for feedback, you already have it. MediaWiki, out of the box, protects personal js, all of it, from editing by others. MediaWiki, out of the box, considers all js in a user's User: space as personal js. The pref is for personal js, not (common|monobook|wikia).js.

And yet none of this still has anything to do with the login widget on every page, which is still there, combined with the global (i.e., not personal) js repository, the actual source of the real problem.