If you do not control the application that sends messages, the application can always do E2E, only to spy on the messages on the end devices and snitch if necessary... We need E2E + no "bonus features", and to ensure both hold you need to review the code.
Problem is those services aren't very user friendly. After all most users want to maintain history, recover their account if they forget their password, and other things not exactly compatible with highly secure communications.
You're absolutely right. I currently develop twonly, an open-source alternative to Snapchat, where I encountered exactly these kinds of problems, such as a passwordless recovery. I came up with the following solution, happy to hear feedback :)
