The idea as stated has been proposed and refuted more times than I can recall.
The web of trust idea, however, while looking better at first, is also flawed. The problem is how to tell who is who between servers -- short of a registry process, there is no way that will work in all cases. And a decentralized registry system would be shitty as hell. A player would either have to register for _every_ server that they play on, or we'd have to again turn to a centralized service, which, as we've stated, won't work either. You can't use GUID to track users across servers, because having a unique GUID for every server is needed to avoid impersonation. (Quick version: Player Foo, who is admin on server Bar, joins server Baz. Baz's admin is a bad person and copies Foo's GUID, then uses it connect as an admin to server Bar.)
TL;DR version: This shit doesn't work. Play on servers with admins.