Digital self-destructing possibilities?

Hi,

What do you see as the range of desired vs. possible things in the
realm of digital self-destructing messages?

* What do people want, ideally? E.g. I send a message to Fred and he
can only see it once and then it is gone.

* What must we accept / can we rule out? E.g. they can always take a
picture of the screen, even if e.g. the display device disables
screenshotting.

* What would be technically useful and/or vs. what would be socially
useful? People might know that the recipient can always just take a
photo, but still be willing to send the message / use the service if
e.g. nobody else can 'take the photo' such as the intermediate
servers.

* Under what contexts would the lock-down just push people to share in
other insecure ways? Or are there contexts where the lock-down is more
acceptable by all main parties involved? (And personally while I can
guess that such contexts might be e.g. a lot of sexting or something
worse, I believe there are still plenty of not-evil contexts.)

thanks for your thoughts.