[tsimionescu]

It depends on the intention. If this is about a unified international community, like a group of contributors to a Open Source Project, or like HN, then there is no reason to allow general unicode identifiers.

If the project is instead a more general solution intended for many independent communities that may well be country-specific, then yes, it should allow general Unicode display names. It should probably still help restrict this per community, so that a Chinese community doesn't get confusables with Japanese-only characters (though Han unification probably happens to protect from that), or a Cyrillic community doesn't get confusables with Latin characters.