The incremental improvements in e-ink contrast over the past several years, and the unchanged 4-bit gray scale, make it uninteresting to me as a basic technology. 1/4 to 1/7th the contrast of paper? No thanks. 4-bit grayscale? No thanks. The tech isn't evolving into something I'm interested in buying into again.
100:1 contrast, 256 shades of gray
, ~300 ppi, and I'm interested. E-ink isn't going to get there, ever, as far as I can tell. Very low power consumption is by far the biggest feature, and that's not enough.