I have a Dasung e-ink monitor. It's great for typing, but you'll have to use a white background to get good contrast

Dasung and Onyx sell e-ink monitors. I recall hearing that some of the high end e-ink tablets have a mode in which they act as a monitor as well. You can find video reviews of them to form you opinion on whether they're responsive enough.

I mean as long as the system is taking inputs it really doesn't matter when the screen shows them to you. Modern systems can still do what old systems used to do and you're apparently not doing stuff in a terminal right? In DOS you could start typing all of your commands while the operating system is starting and everything would be buffered including the enter presses.

Long and short of it I'm just saying don't worry about the screen responsiveness of eink and just enjoy writing.