A low-res display would be fine. In fact the same display as the original Model 100 would be great.
A sibling mentioned e-ink and that might be ideal. With a fast enough CPU and race-to-sleep scheduling, the machine would mostly be in a low power idle mode.
I think the temptation for a lot of designers here would be to use Linux and I think that would be a big mistake. A custom, basic OS with a few simple programs like the Model 100 or Psion 5 had would be ideal, at least for me. Or maybe even something like FreeRTOS (like the Flipper uses) if it is low power enough.
