The idea of an interactive calculus "e-text" sounds exciting. It seems like this could be done in a way that would allow students to figure out a lot on their own (with built in feedback at key points). My calculus students enjoy the exploration and discovery exercises they do with partners, figuring out things on their own before we discuss them and before they read explanations in the book. The opportunity to embed moving diagrams through applets also makes this a wonderful way to allow students to ponder ideas from calculus.
I think it would be exciting and instructive for the students if the text is organized in a way consistent with the development of calculus (fascinating questions provoke imaginative thinking which eventually leads to the development of the concept of limit, definitions and theorems) rather than the sequence found in most calculus texts.