It should be possible to look up global preference for central users without local accounts.
The current use case is T42050, where we want to centralize password resets, which would also allow initiating them on wikis where you don't have a local account. There is a preference that allows you to require the correct email address to be provided in order to request a password reset (added in T234401). We want this preference to apply when requesting a password reset on any wiki, even on wikis where you don't have a local account, so that this anti-harassment feature can't be bypassed.
This could be useful for other preferences that affect how you appear to other users. The main thing that comes to mind is the gender preference (although currently the GenderCache code hard-codes using local preferences only). I also thought of GlobalUserPage, but it turns out that its global preference has been removed (T188423) and it doesn't work without a local account anyway (T162648).