Cheap e-ink devices will probably have their place, but tablets are quickly becoming more capable and cheaper. As they get under $300 and handle almost all of a student's computing needs, it will be hard to justify the savings of a vastly less capable e-ink device (at least in countries that can afford a $300 per student purchase).

Multimedia adds very little to your average Kindle book, but videos and interactive content add huge value to a textbook. Once you add the fact that a student can accomplish coursework and quickly make schools paperless, I think it's a huge value add.