So I'm thinking that we would have prop=globaluserpage which would indicate whether a page that does not currently exist has a global user page shown, and then somewhere expose the API url being used in meta=siteinfo. Does that sound good?

We already have 'imageinfo' which provides 'imagerepository', which is essentially the same concept. If we add prop=globaluserpage, would we also have a prop=globaltemplatepage , globalmodulepage, globalgadgetfoo, etc for every new type of remotely hosted page? I'd hope not.

As the file pages are also loaded from the file repo, unless there is a local page, the new property should encompass that and any future instance where the storage is found at a different API endpoint than the local site. And if the prop is queried on a page which is local, it should use 'local'.

In T89540#1038864, @Legoktm wrote:

So I'm thinking that we would have prop=globaluserpage which would indicate whether a page that does not currently exist has a global user page shown, and then somewhere expose the API url being used in meta=siteinfo. Does that sound good?

Another option would be to add a hook to easily add additional inprops to prop=info, since it seems like the proposed prop=globaluserpage would return just one boolean.

I also like jayvdb's idea of some sort of "prop=foreignrepos" (and a meta more generic than meta=filerepoinfo) that could be used by foreign file repos, GlobalUserPage, maybe Wikibase (to indicate the corresponding Q-page), and anything else in the future that pulls stuff from a remote source. Although that might take a little thought to do right.