> ...if you can't inspect it you can't reasonably trust it.

That is the point the article is making, and that's what it sounds like the Keybase client is doing--not trusting the server by relying on client-side encryption rather than storing keys on the server.

The fact that you can change keys and see old messages without the other party sending them to you using your new key points to serious problems with these other apps. It seems the Keybase client rightly considers the channel insecure.