|I don't know why we don't have paired key support built into browsers, and extensions built for major web languages.|
For users, it may seem similar to OpenID (sign in with google/facebook/twitter, etc.) but the public key could be provided automatically by the browser.
Of course, there may be portability issues, but with the availability and prevalence of smart phones, tablets, etc. and with the increasingly common "browser sync", I'm sure that could be easily dealt with.
So if anyone is working on this, where are they, and if not, why not?