This sounds an awful lot like OpenID (2). What makes it different? My OpenID login (aka XRI i-name) is "=chris.hills" and works on sites that support it.
There's a little more discussion of that over on Lobsters: https://lobste.rs/s/fkosun/. The TL;DR is that URIs just didn't work for the mass public. You had to supplement the login form with a NASCAR-esque wall of logos, which was awful for different reasons.
Thus, Portier, and Persona before it, chose to identify users by email addresses. I talk a little bit about that at 9:05 in my PyCon 2013 talk on Persona: https://www.youtube.com/watch?v=nJff23UdNAI#t=9m05
