Brion Vibber wrote in part:
We may wish to do a case-_in_sensitive check, and/or a same-except-for-accents check. Or not. Anyway, I think it could use some tidying up.
We'll probably never think of every way to mimic a previous user. If there's an easy check to do (and there clearly are some), then go ahead, but ultimately we'll need to rely on policy: If somebody creates a username for fraudulent purposes (as [[Fr:Utilisateur:Anthère]] was), then it should be removed (as [[En:User:Throbbing Monster Cock]] was, for other reasons).
-- Toby