Here is an analysis of the future of the ebook market in education from Warton Business School / China.
The National Association of College Stores estimates that less than 3% of textbook sales today are digital versions …
My reading is that the wildcard in attempting to make predictions is whether new providers (e.g, Amazon, Apple) decide to move into the textbook (and I would suggest learning media) market.
Digital media opens up new possibilities (integration of multimedia), but is presently limited in other ways (ease of highlighting and annotation).