I was thinking I could just get the username from the response of /users/{ids}/associated (where {ids} is the not-site-specific id). But then realised that it returns only network_user (even though we have filters now ?!?!)
Would it be possible to have a network /users/{ids} and network /me route, that will fetch the network profile details. This would make it easier to get a user's overall profile.
Or instead just have /user/{ids}/associated return a full user, and let filters do what they do best.