I'm honestly not sure why the password managers don't offer federated login (with SSO helped out by their browser extension). As a website owner, I'd love to be able to throw a "login with lastpass" link on the sign in page.
OpenID provides federated login and is already widely used. It's not frictionless however and didn't really take off as much as people first expected due to usability problems with login-urls as user ids and anonymity to website owners.
