A quick research shows that all current commercial E-ink devices have a maximum grayscale level of 16. Is it a hardware limitation? Or can we get more grayscales just like we have done on CGA, Commodore 64, GameBoy Color and many other vintage hardwares that have a color limitation?
Well, the answer is yes. See my results :p
Just as said on the screen, happy new year 2018! (The upper right is one in 4bpp mode for reference)