Definitely. I finished the first draft after the JPMS spec was rejected, and submitted the final draft about the time the JSR was finally approved. Everything else in Java 9 was stable, but naturally all anyone cared about was Jigsaw, for good reason.
In the end I decided to include a single Jigsaw example that was more than a simple Hello, World, but didn't get into all the details of automatic modules and unnamed modules and the rest. There are entire books being written just on JPMS anyway, so I'm hoping a primer on the basics will be enough. I also expect that while a lot of JavaRanch users will be interested in Java 9 as soon as it appears, there will probably be a significant delay before the community as a whole adopts it.
Incidentally, I originally hadn't planned on discussing Java 9 at all. I had hoped to finish the book early this year. But as it grew from the original short book (about 25 - 30 recipes and 125 - 150 pages) to its current form (about 70 recipes and 300+ pages), it became clear I had to include Java 9. In the end I'm glad I did, but it did mean dealing with some major uncertainty as the spec evolved.