Depends on how much the overlayed LCD screen would impact legibility. I'm not sure. Transparent OLED might work [1]. The backlit would basically be for evenings, where the ambient light might not be enough. I just love the readability and aesthetics of eInk. Practically, it's probably worse at everything...so I can understand the limited uptake.

[1] http://www.mmt.io/transparent-oled-touch-screen-display/