One problem with distributed systems is the lack of a centralized authority for usernames. (Who says @POTUS is POTUS?) So why not create a custom TLD for a Twitter-like service? Each domain would be required to implement the API for that service. This would solve the username problem, and allow the registar to remove abusive users, but also let users host their own content. The only problem is domain registration fees, but hey, .tk domain names are still free.