I just want an 8.5" x 11" version that is portable, runs Linux, and can open PDFs. For reading papers you wouldn't be able to beat it.
E Ink announces a full color electrophoretic ePaper display | https://news.ycombinator.com/item?id=11766073
https://GetRemarkable.com $480 pre-order | https://news.ycombinator.com/item?id=13113819
(There are a number of other 8.5"x11" eink PDF readers out there.)
I bought one used in university and would use it for reading PDFs. Really slow refresh rate, but who cares if you're just reading big pages?