Maybe I'm missing something, seems like any of these apps that might want local storage for some reason could store data in an encrypted format. A cloud backup

Maybe I'm missing something, seems like any of these apps that might want local storage for some reason could store data in an encrypted format. A cloud backup would then be backing up and restoring encrypted data. Where the user holds the key in some form to unlock the data at the right time. They bring up a good point that anyone with access to the message can leak it, no matter how tight you lock down your side. Something ephemeral seems best if you really want security.