> why bother? Email is just one of dozens of messaging systems available to Internet users. Better to move sensitive conversations to things like Signal, WhatsApp, or Wire --- the double ratchet construction is designed specifically to make IM-like protocols secure even when conversations are sporadic and last months.

This makes me sad. There's something profoundly democratising about the idea of running your own email or XMPP server (or any kind of server, for that matter). It's something you're in control of, that's configured the way you want it. Using someone else's server for everything brings with it a kind of tyranny (even if the people in charge promise not to use it for anything tyrannical (like that's ever happened)). If the response to that is "yes but it's hard/impossible to build a secure, distributed messaging system" then I think that's overly cynical.