You can get refresh on a Kindle screen down to under 100ms if you want plain black and white. You only get the ludicrous refresh times if you want greyscale --- I believe they do some kind of dithering over time to achieve that.

Back in the old days I had a Hercules monitor with slow phosphor. I've tried to find some figures on the response rate, but I wouldn't be surprised if it was a similar speed to the eink screen. It was really comfortable on the eyes and I slightly miss it (of course, it was the size of a postcard compared to a modern monitor). So I think an eink monitor could be quite usable for certain purposes.

The thing I'd be concerned about is scrolling. We've got very used to monitors which will scroll smoothly. I've seen monitors which just turned into hash when scrolling; there's a reason why vi and emacs have modes for page-at-a-time scrolling.