Speaking of "alternatives to e-ink for a zero-power-use-when-not-updating dot-matrix display"...
Has there ever been designed a "display" that is just a thermal printer hidden in one end of a box, and a take-up spool + tensioning spring hidden on the other end, such that the "display" is then a continuous thermal paper "scroll" stretched across the box behind [UV-protective!] glass, that can be "refreshed" by printing a new full-width image to the thermal printer?
If you wanted to take this a little further, you could cover the "display" with heat erasable ink like is used in a Pilot Frixion pens.
This ink is interesting in that it fades when heated (60 C), but darkens when cooled (-10 C). In between those temperatures it is stable.
Thus you could have one loop that is continuously reused. Not sure how many cycles you can get before the ink degrades.
I like that idea. The printing process should probably be inverted: cool the paper as a whole to darken the whole sheet amd use a small heating coil to erase.
Or thermochromic film
https://en.wikipedia.org/wiki/Thermochromism
Ooh, I like this idea. You could also use the box structure to stretch the display so it has 4 sides if you build the mechanism correctly, which means as you refresh the image on the "primary" display it moves the other images to the secondary, tertiary, and quaternary displays before it gets taken up. You can use tensioned rollers at each corner hidden by the frame if you plan for a gap for "bezel".
Allow me to correct you: Some fax machines use thermal paper so your display can be at least 8.5".
Not sure if you can call it a display if you have to throw it away to change an image.
Look into ticker tape, and dot matrix printing, this is how early computer displays worked.