Ebook retailers have noticed that customers who have a dedicated [e-ink] ereader read faster, read for longer, and -- most importantly -- spend more on ebooks than customers who don't.* As long as that remains the case I think e-ink readers will continue to be developed and sold, at least by those retailers whose main business is ebooks.
* E.g. see "What the platform tells us" in
Kobo's April 2016 report.