With almost everyones backups stored in plain-text, making it all a little silly.

Think about it for a second: you can re-establish your WA account on a new device using only the SIM card from your old device. SIM cards don't have a storage area for random applications' encryption keys, and even if they did, a SIM card cannot count as "end-to-end" anymore. Same goes for whatever mobile cloud platform those backups might be stored on. And you'd hope Apple or Google aren't happily sending off your cloud decryption keys to any app that wants them. Though maybe they are?