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When reading, e-ink puts less strain on your eyes. There is also a battery life advantage. However, current e-ink readers are mostly low on functionality and black/white.
High contrast mode also puts less strain on your eyes...and let's you read on a phone or tablet, which has a lot more uses than a dedicated device. The background is black and the text is white.
If the eye strain benefits are similar then this would predict a very small market penetration for dedicated ereaders in the long run unless they figure out color e-ink...although this might not change the conclusion either.
Thoughts? I encourage you to read your next novel in high contrast mode on a tablet and report back on the eye strain and reading speed vs a Kindle et al.