The only way to approach a comprehensive "history" of the genre is to (a) look at it from a global perspective and (b) remove the limitations of what constitutes the genre. I can't begin to count the number of Internet arguments over "ambient doesn't have beats" "oh yes it does." I find it more than a little funny that those who claim ambient can't have beats seem to have no problem with placing SAW II in a top ambient of all time list. Anyway, my point is that any book I would undertake would include not just Eno-derived works and the various rhythmic ambient offshoots, but also the cross-pollination with both spacemusic (Serrie, Tyndall, Braheny, et al.) and "new age" (i.e. artists like Story and O'Hearn whom most "ambientists" don't recognize as ambient). The book would probably best be structured as (1) first a brief pre-history of the genre, which would mention Satie, et al., (2) a brief chronology of the history of ambient recordings starting in, I would guess, the 60s, (3) a section of the book detailing the different global approaches to the genre, (4) a look at crossover genres (see above) and (5) essential artists and recordings (basically "if you want to start an ambient collection, here are the albums you need to get). Finally, the last section would probably be devoted to the surge of popularity of netlabels, download only releases, and the "future" of the genre. This section would almost certainly be comprised heavily by interviews with notables in the scene, such as Mike G and other label heads, as well as noted critics, Lockett, etc. Of course, one cold also get into a history of the electronic side of the music, i.e. how the first synthesizers came about, their development, sequencers, the digital revolution, laptop and glitch, etc. But, shit, that could a volume all by itself, so it would have to be, at best, a cursory overlook, IMO.
You start to see why this would be a massive undertaking if the author had any intention of posturing the book as either a history or comprehensive. It may make a lot more sense to do a collection of essays, kinda like the two Lester Bangs books, Psychotic Reactions and Carburetor Dung, and Main Lines, Blood Feasts and Bad Taste. If THAT was the case, the essays could be a multiple author collection, featuring a number of my contemporaries and myself. I would be ideally suited to address the cross-over genres, as I'm sure others would be better with contemporary ambient, the history of netlabels, etc. The only problem with this approach (and it is the ONLY problem I can think of) would be that the reader would be confronted with VASTLY different writing styles. Just compare my style with Alan L and Darren B and you see what I mean. OTOH, my style meshes nicely with John Shanahan (Hypnagogue) whom I think would be a great person to bring into this IF it ever reached the actual planning stages, as well as Phil Derby (the perfect person to chronicle Berlin EM). Another obvious person to include would be Richard G and others who contribute reviews here and elsewhere. The logistics might be problematic, i.e. deadlines, etc. But that would be the domain of the book's editor.
Hoo boy...I am putting way too much work into this!
That's how I would see it, at least.