Would it not make a lot more sense to load a users' global scripts from its home wiki, as designated in Special:CentralAuth? I am rarely on meta, so requiring users to store their global code there seems overly complicated.
Topic on Extension talk:GlobalCssJs
Nope. Or at least this is something I wouldn't be able to see as an improvement until CentralAuth has a way to set your home wiki. MediaWiki.org is my home wiki in terms of edits and user rights and overall activity, but CA thinks my home wiki is test.wikipedia.org, where I have a whopping nine (!) edits and some user rights. So no, I wouldn't want to have my global CSS & JS stored on test.wikipedia.org; Meta in the context of WMF wikis makes total sense to me as it's a central place for coordination.
Yes, what Jack said. CentralAuth has some unreliable criteria with which it picks a home wiki, and it's really only used to figure out who wins the account. Also, from a security perspective it is much safer to only allow meta admins to edit your global scripts, as opposed to any testwiki admin :/.
+1