I spend all of my days reading PDFs.

I want an 8.5x11 device with large-size microUSB. Nothing fancy, no markup, no net connection, huge battery. Simple page turning (could be touch or button). Simple file handling. Memory of where I stopped reading.

You could sell these things in volume, the first venue being libraries and bookstores.

Students with school library access could use them to carry all of their papers. Profs could use them for research.

Sci-hub would be a perfect research match.