I honestly don't like the idea of centralizing / federating such a system. One bad actor and bad management of backups, yikes... In fact, nowadays, most people don't even have valid backups (that automation can't tamper with). This doesn't even get into anti-tampering, i.e. GPG signatures and the like.

Outside of that, I believe that every nation would have to agree (hah!) on some naming or ID standard.

All of that said, I think it would make sense for small communities to have a master-master LDAP setup for all their web, chat, various apps, forums, etc. i.e. Keep things off facebook and google.