The author makes a very good case for why this approach won't threaten password-based authentication, including:

...hard for first-time users to get right:... The private key being unlocked and available via ssh-agent.

For this to be convenient for daily use, ssh-agent is essential, and that could expose naive users to compromise. I know enough to disable ForwardAgent in my personal config by default and generate site-specific keys for hosts I can't trust, but that's beyond most ordinary users and even many of the technical professionals I deal with.

It's a shame PGP was the target of so much persecution when it came out. Maybe by now we would have worked out the key exchange problem and would all be enjoying personally encrypted communication on the Internet. I sometimes feel that any attempt to move beyond passwords without realizing that ideal is doomed to failure.