@dside @delta @qyahxm Here by reliable deletion they mean that encrypted copies can not be later used to get the original message. Do see the interesting talk where they discuss this (and also say the same thing about control of other devices): https://autocrypt2.org/#/
The only thing I think is saddening is that some people think that "reliable deletion" *should* include some guarantees of plaintext and key removal by all parties. No, it's still useful without that guarantee. And ideally we should have a toggle in the app that actually turns off the behavior of deletion of plaintext. Maybe then people will stop assuming this can't be done.