In fact, the reading device i'd favour the most is already in the making:
www.pine64.org/pinenote
wiki.pine64.org/wiki/PineNote
It combines the 10.3" sized e-ink screen of recent LikeBook/Onyx Boox devices with that same form factor with a much more potent computing platform.
It will eventually evolve into something much more useful than just a passive reading device, thanks to the flexibility provided by a truly open platform.
Nonetheless, i doubt this will ever be suitable for users merely defined by a consumer mindset. But for people who prefer open devices whose capabilities are only limited by one's own competence and imagination, this is a worthy investment target.
I am already a happy user of the same company's '
PineBook Pro' running a feature complete Debian environment, serving as my daily driver.