I have been asked a few times since Rails 5 was released when Rails 5 in Action (an update to Rails 4 in Action) will be published. The short answer is that it won’t be.
After Rails 4 in Action, I cut ties with Manning due to problems I’ve outlined in many previous posts. Most recently “My self-publishing success story”. It just isn’t worth any more energy/time to continue to work with that particular publisher. Since they are the ones that own the rights to the Rails * in Action series and the IP of the book, working on an update to Rails 4 in Action would mean working with the publisher, and that’s not something that I would choose to do again.
Couple this with a 3-year “no-compete” clause that means I won’t be able to publish any book-length Rails beginner content. So even a competing book to Rails 4 in Action is out of the question (at least for the next two and a bit years).
So Rails 5 in Action is never coming out. Rails 4 in Action’s code will still work with Rails 5 (mostly) and it’s a valuable demonstration of how to build a decently sized Rails application.