Not to burst your bubble, but the UML idea may not be the right way to go. Assume you are going to be sending this document to several people at a publisher, so you want a format that everyone can easily use (without having to download viewers, etc).I think have UML diagrams will still be useful, even if not for the TDD. Plus we can export to GIF, and embed into the document.
I'll look at the document today and give my 2 pennies worth. Also, if you are looking at a way to have it as a living document, we should put it up on the Wiki site so all can work on it there, rather than send it around via email (as it is generally less protected).
By that do you mean uploading lots of Word docs, or using a Wiki page?