I only read books that I have a physical copy of, or books that are on project Gutenberg. But really, we should seek to make all books free. An unencrypted epub is like 1 MB for like 300 pages usually.
I do wish that there was an open source e-reader that ran Linux. You can already read these things on your phone or on your computer. But I like the dedicated devices for reading.
Someone made an open source one that runs on a microprocessor, and it is a super cool project. But you really need a kernel to run arbitrary code, and gain access to open source e-reader software that gets you compatibility with publishing formats, layouts and fonts.
Getting Linux kernels onto more open source devices is probably a good goal - its still rather hard for a hobbyist to design a devicw that supports Linux.