I wonder if there's a KOReader oriented OS for the Kindle, to go beyond jailbreaking it (it's nice, but a bit clunky to me)... There seems to be an Android port for some models so it should be possible.
So there was: InkBox OS, mostly for Kobo but with some Kindle support, it became QuillOS (wirh the same focus on devices) but when Kobo went with secureboot the whole thing moved to the PineNote. But all of that is very outdated now...