Shame
I looked at Persona a few years ago when the Mozilla wiki and bugzilla switched to it. Technically it's quite nice and easy to implement into existing applications. I considered creating an LDAP-Persona bridge in PHP to allow a couple of the organisations I still unofficially sysadmin for to sign in to internal stuff with corp creds, without having to making LDAP available and tunnels etc.
The downside to Persona was that it is decentralised. The money-makers of the modern web aren't particularly fond of decentralised.
I ran my own OpenID endpoint (provider?) for a while which was great apart from most services just use OpenID for initial sign-up then just keep a copy of your e-mail address etc locally anyway. Instead of storing the OpenID endpoint. It seems this is often the case with the sign-in with Google/Facebook/Twitter brigade too, you usually end up being funnelled through the process of creating a local account with the third party anyway.
Sadly there's more money in flogging e-mail addresses than OpenID endpoints or OAuth session keys.
One of the nice features of OpenID (possibly in v2 IIRC) was that you set things like usernames, forum nicknames, locations, timezones, avatars and any other metadata locally on your endpoint then the 3rd party service grabs and updates that data when you login.
Edit: I can believe I spent 10 minutes writing about Persona. I need to get out more.