There are a few commercial products popping up and marketing. I think youll find what you find here interesting: https://old.reddit.com/r/writerDeck/
Im using a Boox palma 2 on a stand, and a Thinkpad Keyboard 2 to emulate the same thing. The battery life may not be 100 hours but considerable.
I'd love something ipad size with an attached keyboard/trackpad that did the very basics of compute but on a more modern stack. I think the biggest thing that would hold me back would likely be the slow refresh rate/no color in the display. I bet a setup like that with solar so is trickle charged could be built and have an effectively unlimited runtime. I wonder when high refresh rate/color e-ink like displays will finally make it?