[JoshTriplett]

> Strong, deniable, end-to-end encryption should be mandatory.

Strong end-to-end encryption with perfect forward secrecy should be mandatory. Deniable authentication (https://en.wikipedia.org/wiki/Deniable_authentication), however, seems like a potentially interesting option but not one that the protocol should mandate. Sometimes you do want authentication that remains valid after the conversation ends, so you can subsequently authenticate the messages in it.