So, yeah. Zoom did bad stuff. But Keybase is designed so that all those things would obviously be detectable (Keybase client code is open source), and the ways in which the Server could mess with data are much restricted. If that spreads to Zoom, there's a chance it'd be a good service in a year or two.

PGP keyservers have a fundamental issue that demands a solution like CT logs or Keybase-style merkle trees.

The only way to prevent getting Loki backdoor issues would seem to be a development so clearly in-the-open, that any secretive addition of significant code/suspicious PR behavior is obvious.

Tor does not use Tor by default. It works with Tor, but that's it.