Giving new life to an old eReader using solar power is as optimistic an image of the future as I can get right now. There are dozens of us... DOZENS! Ditto for the build-your-own kit.
I really enjoyed the work you put into finding the best images for the medium. It matters! For instance, I noticed that in the black-white-red ePaper, photos with a subject containing a lot of red hue really pop out. Container and content should always go hand in hand.
Some e-readers can run mainline Linux, making this super easy to build. Specifically I'm working on a UI for the Kobo Clara HD: https://github.com/bjesus/air
Perhaps, instead of a polished version, you could sell the components as a kit?