What I see as being a useful book on Flask:
1) listing and naming common stable plugins (flask-security, flask-login) and how they integrate and work together. There's a good page on the Flask site, but I feel a lot of the plug-ins don't work particularly well together. There's tons of different authentication librarys (especially when dealing with OAuth) that work with varying degree out there. Some guidance around this would be really useful.
2) Different ways to setup a large project. How to structure folders, etc. There's some good topics on StackOverflow about this, but my experience trying to integrate different plug-ins, etc, leads to a more messy solution. Maybe some ideas in abstracting out data access.
3) The Art of building up your tech stack with lego bricks. Choosing which plug-ins to use.
4) Testing patterns.
5) More of a style of "I'm trying to do this", this is how you do it. (Note: there's lots of great questions and solutions on the email list that could/should be culled for ideas and consolidated)
6) Debugging and tracing through 3rd party flask-plugins. This is a huge problem for me as most don't include log comments
7) Writing and structuring a good plug-in/blueprint, with some examples of different ways to include reusable code into the project.
Note: I've co-authored a book in the past that was published by Wiley and I think your schedule is pretty optimistic, especially considering you've still got some learning and research to do. Unless, you're just regurgitating the already pretty in-depth documentation.
Second Note: I'm just reading the O'Reily book on Angular.JS, it's less that 200 pages. It's dense with ideas and explanations on WHY something is. This makes it extremely useful. I really like books that focus on the WHY, because the HOW because much simpler to comprehend. I also appreciate the book because it's not some 600 page tome of regurgitated documentation.