There are, and have been, a fair number of attempts at E-Ink phones (O-B themselves had an earlier attempt, the Midia, back in 2014 -- but it never made it into production).
This site provides a list of a number of them. The most successful of them (i.e. the ones that engendered follow-up products) appear to have been dual-screen phones.
I rather suspect that there is a fairly wide difference between a "definite market" and a
profitable market.