If someone could use your public SSH from say Github and send you a private message that would be great. From my understanding that is not possible. You need to generate and exchange PGP keys before, a major UX issue. Allow SSH public keys to be used and we'll be a lot closer to fixing the secure email issue.
Also Facebook (which has an official onion site to help if your internet connection is suspect) has GPG as a standard part of all user profiles. This would be a much more normal person directory than GitHub or MIT ( yes someone on HN suggested MIT as a mainstream PGP directory)
That's pretty much what https://keybase.io does, in a roundabout way. It links your public identity across many social networks to a PGP key, so you could say "let me talk to kstrauser on GitHub" (or on Hacker News!) and it would map that back to my public key.
