Hacker News Reader

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)

Friends (https://moose-team.github.io/friends/) allows you to use your SSH keys but it's not email anymore.

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.

But they can, it's just not PGP.