Yet another stab at trying to solve identity on the internet. The problem this will face, just like every other attempt, is that websites want to own their log in process and associated user records.
The only people that benefit from single sign on are websites that experience high friction on sign ups. i.e. "oh I need to create an account for this?" and close the browser tab. In which case a Twitter or Facebook button makes a lot of sense.
I highly encourage anyone looking to build something like this as more than a fun side project to read up on the fascinating history of Microsoft Passport.