I should preface this by saying that my experience with e-books is still very limited, but it does occur to me that we still haven't really taken advantage of available technology to provide a book reading experience any different than just viewing the same printed page through another medium ... and from what I glean from online reviews, even accomplishing that first generation paper-to-digital formatting is immensely problematic for many.
In the Civil War publishing world, it appears that Savas Beatie will be among the first to dip their toes into this pool of unrealized digital potential. For their upcoming new edition of the Richard Sommers classic Richmond Redeemed, the publisher has teamed up with a content technology outfit called Olive Software to create an interactive e-book version. According to the Savas Beatie press release, using Olive Software's proprietary platform called SmartLayers the "digital edition offers scores of icons and links representing photos, further reading on related subjects, videos, and, most important of all, original author marginalia in the form of dozens of comments, assessments, and additional insights and information keyed to specific personalities, combat, tactics, and decision-making."
With a reading public trained to expect sub-$10 e-books [though serious Civil War history books are frequently priced substantially higher], one wonders how quickly premium priced "enhanced" e-books will catch on, if at all. Another question mark would involve the willingness of today's non-fiction publishers to allocate the time and dollar resources necessary to do this right while at the same time fulfilling their other more traditional duties. Surely this type of thing will become commonplace at some point, the only uncertainty being when.