The main problem with Persona was not the tech, Persona is great and works well. The problem is that building federated identity services is hard. Persona is not a centralized login system such as "login with Facebook". With Persona, once you decide to login with your email account, first Persona looks for an IdP with your domain/provider, the if not found it goes back to the persona catchall service. For a while gma…
This implies a classic chicken/egg dilemma: email providers won't implement Persona support unless that would be useful for lots of people; Persona wouldn't be useful for lots of people until their email provider supported it.