The e-book format has inherent multimedia possibilities: trailers, background and reference materials, interviews, actors reciting the poems the book contains. But will these ultimately be considered enrichment of the text or just distractions from it? Perhaps these sorts of experiments will go the way of Flash splash pages and manically hyperlinked documents. In the end, the portability may be the fulcrum, the only fulcrum. Are e-books simply the paperbacks of the future, the cheapest way to publish the cheapest books for the largest number of readers?
I tend to think the last question is the most important as well as most easily answered. Sure, there will be books with ancillary bonus features, but I think people will view that kind of content as they do the bonus material that accompanies some DVDs. There will be some opportunity for authors like Mark Danielewski to take advantage of these feature in avant guard ways. But mostly, eBooks will be cheap, light, and easy to buy, just like mass market paperbacks are now.