Any book, however large, can only cover a small subset of the vast collection of topics that comprise macOS development. With the material in this book under your belt, you should be well placed to make best use of the huge pool of resources out there, although it is often hard to know where to start (and what to skip).
Accompanying this book is the following website: http://grimshaw.de/macOS-book.
This includes a (very subjective) list of resources for further reading and study, one that I hope will grow with time.
It covers several topics that would have been great to include in the book, but which didn't make it for reasons of space.
It will also record any errata and clarifications, as well updates to the code that become necessary as Swift develops, and there'll be a link through which you can submit feedback on the book, and any suggestions for inclusion on the site itself.
I hope that reading, and working though, this book has been both enjoyable and rewarding...