Yeah, to me, this is the most important response. In theory, you could layer an email UI over a federated secure messaging protocol, like Matrix's E2E or XMPP+

Yeah, to me, this is the most important response. In theory, you could layer an email UI over a federated secure messaging protocol, like Matrix's E2E or XMPP+OMEMO. In practice, no one has done this, and infosec people only seem to care about instant messaging for some reason. Besides all of the points you make above, Signal Desktop is terrible. I often want to use it to avoid typing on a phone keyboard, only to find that the experience of using Signal Desktop is actually worse than that of typing on my phone.