Yes a failure in the voltage creation for the eink display could be one of the most plausible mainboard failures that results in your error descriptions too.
Please keep me informed, sounds like I could learn a lot about by your project.
Eventually this could be helpful too:
https://www.synacktiv.com/en/publica...-reverser.html
This too:
https://linux-sunxi.org/PocketBook_Touch_Lux_3