While this looks kind of interesting, I've seen a large number of things that fall into this vein, and a few concepts seem to be missing (conflict resolution being a big one). Independent of that, though, when I first started working on my book, there were two tools I quickly needed but could not find. The first being a way to save references that linked outside of the document without being part of the document (think fact checking, reference materials, etc.). The second was a way to edit the document(s) and be able to compose sections/components together at a high level. I ended up using muse mode for emacs and fossil as an VCS (the wiki is particularly helpful for collecting resources). What I ended up doing is several files on different topics, then one for each chapter and then one for the book as a whole. Then it's versioned text copy and pasted between files. If anyone has a better system for linking to references and managing the structure of the book, I'd love to hear it.