The first draft is already 90% complete and the book has been sold to the publisher. The decision to write this book was taken months ago.
What's wrong with testing the waters? I wish all writers would do the same. Writing a book is a huge undertaking and any insights you could gain beforehand are welcome.
That would be such a tight schedule...surely they would have something in draft form at least. If this was someone's fulltime job, maybe I could see it, but really there's no reason for them to "test the waters". That was done with their blog, and also HN where you see the topic come up quite often with lots of discussion.
That seems unlikely. They already have a rough time that's not too far off and a publisher lined up.