A few days ago, PixInsight version 1.8.6 was released, with a quick bugfix release following it. At the time of typing this, we are on version 1.8.6.1448. This has brought with it several new things, highlighted in detail in this official forum thread. Following installation, you will need to reactivate your license as they made changes to the licensing system. The purpose of the tutorial update however was because SubframeSelector was officially made a process rather than an included script.
The major graphical user interface revamp required I update the tutorial on pre-processing images, specifically section 5, for calculating optimum weightings for exposures and appending them to use in stacking. The tutorial is now up-to-date with PixInsight version 1.8.6.1448.