I'm not sure if I would say the colour e-ink screens aren't market ready. They do display some color after all. If there is a clearly defined customer target then it could be fine (eg. textbook reading). If you expect it to supplant lcd screens, then of course it isn't ready.
I think colour readers haven't caught on in the educational field because the softwares of those devices aren't market ready and they are way too expensive. 500€ for the jetbook 2 is equivalent to the cost of a laptop, which a student would still need...