Definitely agree with you.. this was just a concept for me that I was able to build with off the shelf parts but this is exactly the type of discussion I was hoping to get going..
A polaroid picture that starts playing as soon as you attach it to a suitable power source (please make it something standard like an AA battery or USB cable), on the other hand, is something you can keep in a box in the attic for your grandchildren to find after you're gone. It's not just a display, it's a read-only snapshot and air-gapped backup of a moment of your life.
Unlikely, unless it's very carefully engineered. For example, the flash life of most microcontrollers is measured in decades.
But that's only necessary if you can't get hold of a source of electricity (such as a wireless receiver) and a voltage regulator of some sort (likely to exist as part of said wireless receivers).
In the past we've had problems recovering data from magnetic disks and the like, but powering ancient devices with simple power input requirements have not generally been very hard, and it's not likely to become so anytime soon unless not just every computer but every lightbulb, kettle, electrical oven and every other little appliance suddenly start receiving energy in a fundamentally different way.
I wouldn't be surprised if they were still around in a few decades' time - there's simply too much cheap consumer electronics out there relying on AA for it to make sense to introduce a new standard. (Energy density is likely to keep increasing - but as for the form factor itself, I suspect it will outlive me.)
There are many enemies of electronics: water, bumps, component failures, etc. that make long term non-specialized storage likely to fail
The trend is, and I believe will continue to be, not using your own memory for long term storage. It's a nearly impossible task. If you're storing anything important on a single device, be it a single use display, or a cellphone, or a memory card/disk, you will lose that data, 100% guaranteed.
We're already moving towards transparent backup of all user data. This trend will continue, because people will become more and more aware that they can't save their own data.