Persona works like email because every identifier is an email address, not an opaque OpenID URL. You don't have to have the NASCAR-esque "Sign in with OpenID Provider X, Y, or Z" login page if users can actually use an identifier that that already know. :) (To be fair, OpenID Connect is working on fixing that problem)
> I just hope those advances turn into an open protocol someday.
You're in luck! :) The protocol is open and completely decentralized: https://github.com/mozilla/id-specs/blob/prod/browserid/inde...
Mozilla operates a few centralized services to solve the chicken-and-egg problem while bootstrapping, but they're completely optional, and they automatically fall away when a browser or email provider have native support for the BrowserID protocol.