Have you tried the PineNote yourself? It $400 and says that it's "aimed at Linux developers with an extensive knowledge of embedded systems and/or experience with mobile Linux." The community provided firmware they link for it hasn't been updated in over a year.
The Kobos don't limit what you can do with them either, you can sideload alternative e-reader software like KOReader that improves on the built-in reader functionality.
The Kobos don't limit what you can do with them either, you can sideload alternative e-reader software like KOReader that improves on the built-in reader functionality.