SSL Client certificate authentication has existed in browsers for a long time. Browsers even have built in key generation, but noone uses it. Probably because the UI is not very good.
Mozillas new BrowserID scheme is pretty similar to this too.
PKI as implemented by SSL Certs is needlessly complicated, which is a big part of why no one has adopted it for end user authentication. Compare what I described above to the mess described here: http://en.wikipedia.org/wiki/Public-key_infrastructure
A decentralized key system as ssh provides is much more appropriate for end users.
Mozillas new BrowserID scheme is pretty similar to this too.