I tried using my phone in grayscale mode for a while, but the complete lack of colours makes it difficult to use.
I'm working on making a "desaturated" mode that changes the android renderer to not go fully grayscale, but only a little, so there's still some colour information.
I was always taught that a design should be done first in greyscale to make sure that it works well using only alignment, hirearchy, balance etc, then you add colour; I still see that done frequently in print design, but less so in the digital world for whatever reason.
the issue with "apps are designed with e-ink UX in mind" -- how many stock apps do you actually use? where the manufacturer has control over how it's implemented?
Usually the apps that are used frequently are apps that are designed for big colourful phones. That's why i want to experiment with a "deglossed" or slightly desaturated version.