I agree with your assessment about key change management. With that said, I do like the device history trail that Keybase uses. Keybase has a better multi-device story - in that it has a multi-device story at all. I understand what they're trying to do preserving message history - I do prefer my conversations to be ephemeral by default.

I'm OK with the compromise that Signal has made with key management -- there are people that I really care to have private communication with, and people who I prefer to have private communication with. I verify the former, and don't bother with the latter unless we happen to be bored together in the same room.

On a side note, thanks for your efforts over the last two years!