The community college classes I've been taking lately don't require textbooks. It's more like they give you a list of recommended reading and printouts. So in my experience, I would say the textbook is dying. I've only bought two for $40 in eBook format for this certificate I'm doing. This semester I have to buy another two that will cost me about the same.
It's pretty sweet being able to buy the book right there and then in the classroom.
Not sweet is the tuition going up again.
I'm paying the amount for one class that I did for two the year I started.
So far everything's a Kindle Edition though. Haven't had to buy any PDFs yet, but then I'm not studying to be a doctor nor have I done the basic curriculum since my entry test scores don't let me.
Overall my experience has been that e-ink works poorly for them, even when it's a black and white storyboarding guide. You're better off with the Kindle Fire, iPad, or another Android tablet. The bigger, the better.