I think that at some point in the future (after DNSSEC takes hold), FQDNs will be used both for identity and messaging (both realtime like IM/voice and non, like email). We're already seeing some of this in the form of *@personaldomain.com addresses.
I think that most people's FQDNs will be third-level or deeper, granted by some identity provider, though once the whole user@host format is abandoned I'm guessing that there will be lots of identity/email providers that allow one to one-stop register a domain and integrate it with the service (something that's beyond most casual users of email today).
I thought one of the big lessons of OpenID is that the non-technical world thinks FQDNs are for web sites (or something you type into Google!) and user@host is for identity? I still have trouble explaining that jay@jay.fm is my entire e-mail address, and that there is no .com at the end of it.
I think there was a point where everybody wanted to blog, and thus might have an URL that they considered "me", but that's gone away with Twitter and Facebook. Come to think of it, many people have a Facebook claimed URL, but I've never typed or clicked one, and I don't even know my own.
I wrote about this a while ago: http://sneak.datavibe.net/20100227/the-future-of-the-interne...
I think that most people's FQDNs will be third-level or deeper, granted by some identity provider, though once the whole user@host format is abandoned I'm guessing that there will be lots of identity/email providers that allow one to one-stop register a domain and integrate it with the service (something that's beyond most casual users of email today).