For those of you who want to publish textbooks, is there a way to make this work in your favor? Are there ways you can think of to make your proposed textbook intelligently (rather than arbitrarily, I suppose) interactive? Think about it -- you can have more maps and images, alternate text, audio. This represents a serious change, but also (possibly) a serious opportunity.
NB: On this piece, the comments section has some interesting tidbits (see the bottom of the article accompanying the audio piece), and are worth reading.