Yes the book will probably be mostly relevant technically. But from a marketing point of view, it's dead. If I know nothing about phoenix, I check the website

Yes the book will probably be mostly relevant technically. But from a marketing point of view, it's dead. If I know nothing about phoenix, I check the website and see that the current version is 1.4, am I gonna buy the book that covers up to 1.3? Re: my comment about release cycle, you're right. It was probably more applicable to elixir than phoenix.