Unix was originally designed to work on teletypes, which are even slower and higher-latency than e-ink.
Having used an e-ink device heavily for over a year, including both local (Termux) and remote (SSH) system use via it and a keyboard, I'm conveninced that for text-heavy work it's fully functional, and would probably be viable with a sufficiently-thoughtful GUI which adhered to the design principles and respected the imitations of e-ink:
1. Persistence is free.
2. Pixels are cheap
3. Paints are expensive
4. Refreshes are slow
5. Colour is limited to nonexistent.
6. Pagination over scroll.
7. Full refresh (of page or portion) over pan.
8. Reflective rather than emissive.
9. Minimise animation.
10. Line-art or halftones over shade gradients (images).
That's essentially older GUI desktops before GPUs did more than just provide an interface for the monitor. Paints used to be very expensive (and remained so for quite a while). Pixel scrolling also took a while to appear on consumer desktops.
For older computers, the limitation was in the graphics card itself. Monitors could respond limited only by scan and refresh rates, typically 60--120 Hz, possibly better.
For e-ink, it's the electrophoretic display itself which imposes lag. It's a bit like pushing a wet noodle or a heavy arm. No matter how fast the graphics card is responding, the physical display simply can't keep up and iposes inertia on changes.
Again, for text-heavy applications and reasonably static imagery, this isn't much of a problem.
Current displays can cycle between refresh modes, and it's possible to trade image quality for response time. Presently that's only possible for the whole display at a time, but I might imagine it would be possible to zone a display such that a portion is at a high-fidelity mode and another at a lower-fidelity, higher-refresh mode.
If the idea is for a low-distraction device, I'm not sure that's actually the direction you'd want to go in, however.
> For older computers, the limitation was in the graphics card itself. Monitors could respond limited only by scan and refresh rates, typically 60--120 Hz, possibly better.
If we go really old, we start getting into really slooooow phospors. It would take multiple seconds for a blinking cursor to fade.
Or ink latency. (Best latency.)
Or punch cards.
Or toggled programs.
Or jaquard cards.
Or ...
The discussion above was of the 1990s. Displays were graphical and bitmapped, not text. I remember when dragging and resizing windows with contents visible became A Thing.
And yes, I used computers in the phosphor age. And just a tad during the teletype period. I don't think either applies, though e-ink does have some characteristics of phosphors in terms over overall response rate.
The main distinction though is that phosphors painted in a line, not a full-screen refresh (though it might be interesting to see just how e-ink does refresh in super-slow motion), and then decays.
For e-ink, the characteristic is that higher-quality refreshes take longer, and that a full flush (blacking then blanking the full screen) creates a marked flash. It's much better on recent high-end displays than on, say, a ten-year-old Kindle. But there's still some of the effect visible.
Much less a problem when paging, or when there's a single cursor-point-of-change when typing text. More a problem with complex dynamic displays.