Not the author and not exactly the right place maybe but I saw this on hackaday and there has been some progress on the reader.
https://fread.ink/
article:
https://hackaday.com/2018/07/25/hope...for-e-readers/
It works as an alternate OS and should be unified for all readers, but this is where I think most people will use it. Currently works for kindle 5, but should be ported eventually.