Why not use monochrome LCDs instead of E-ink?
Thanks to a different recent question, I found that it has been tried and is called "memory LCD" and is used in the Pebble smartwatch.

The key is that normally LCDs are driven by a pulse every refresh period, and will fade if voltage is not maintained across them. Sharp have addressed this by adding to the conventional thin film transistors a memory element of some sort. Their power consumption for static images is very small, although not zero.

I think the LCDs are still necessarily glass, while e-ink displays can be slightly more flexible. This is a fragility disadvantage.