I've been working on a demo of something similar. It's a work in progress, but I've got it running at http://nopassword.alexsmolen.com. Code at https://github.com/alsmola/nopassword.

Not only can you register and login with only and email, you can review and revoke your active sessions.

People who are complaining about the speed of email - the session could last indefinitely until you log out, which would reduce the number of times you had to perform the ceremony. Plus, think about the benefits of this when you need to authorize a TV, phone, etc. You can simply visit a link in your email instead of copying and pasting or typing in those form factors.

I'd also like to integrate SMS to support optional dual-factor authentication, which should get help fix the single point of trust problem.