Preface to the 2nd printing of the 2nd edition
What you are reading is the 4th version of this book. Working with MediaWiki was originally published in November 2012. A "2nd printing" of the 1st edition was released in April 2014; it had substantial changes and fixes to the content. The 2nd edition was then released in March 2017. It was even more of an overhaul; most notably, it removed most of the content about Semantic MediaWiki, replacing it with a chapter about Cargo, a simpler alternative to SMW that had been released in 2015.
In keeping with the pattern so far, will the next update to this book be a 3rd edition? Not necessarily. The change to a 2nd edition was motivated in large part by the switch from SMW to Cargo. There has not been a change of that magnitude since then, and in fact, the set of changes in this version is smaller than the set of changes in any of the previous versions (despite a longer time gap), suggesting a maturing of the software. So it could be that the book will stay on the 2nd edition for a while. Still, as is often the case with software, you never really know when the next big change is coming.