Not to diminish the difficulty, but the macos kernel is open source, so at least they have a reference there:
https://github.com/apple-oss-distributions/xnu
(I don’t know how much value that has in practice, but I assume they can at least see how it interfaces with the hardware)






https://youtu.be/nHbA2-_qzH4
According to that channel, eink displays are fast, but the controllers have been optimised for power saving.