The only issue I see is typing fast could get frustrating given what I experience just typing on my kindle. Though maybe the applications and user habits would adapt around it to limit keystrokes and be more efficient.

Or they'd just attach a small digital output screen akin to those old typing machines that you'd then push to the main screen when done. Still wouldn't use much of the battery at least, but would look ugly.

the main issue is the refresh rate. A while ago there was a kickstarter for the Hemingwrite [1] which looked to be heading down the right path.

It's surprising to me that the Yota phone [2] design didn't catch on. Having both a normal screen and an eink screen would be a killer feature, since most of what I do with my phone is text based and doesn't require any color.

[1] https://www.kickstarter.com/projects/astrohaus/hemingwrite-a...

[2] https://yotaphone.com/gb-en/