Have you looked at https://remarkable.com/? It's a little smaller, 12" diagonal.
Dasung sells a 13.3" e-ink monitor: https://www.amazon.com/Dasung-Paperlike-13-3-E-Ink-Monitor/d...
Can anyone comment on the difficulty (for a hacker) of using Remarkable with Kindle books? I have a Kindle already, if that makes a difference in generating DRM-free files of content I already purchased reading rights to.
I have never been able to get EPUBs to reliably work on remarkable. My solution is to convert them to PDFs.
You can also install KOReader on remarkable as a reader. Works better IMHO. https://github.com/koreader/koreader