Windows PowerShell is an established language. Over the years, it has become increasingly important to Microsoft Windows-based services, and of course, cloud services such as Azure.
PowerShell Core represents a significant step forward; PowerShell Core expands out to Linux and macOS, opening up more opportunities to use the language.
The move to open source with PowerShell Core has opened the floodgates for new features, tweaks, and fixes. This is clearly where the future of PowerShell lies. Fortunately, the lessons learned using Windows PowerShell are transferable.
PowerShell Core is great but, perhaps, not quite ready to completely replace Windows PowerShell. Module developers need to test, update, and in some cases rewrite modules to make them compatible with PowerShell Core to complete the move. Much of this work must be undertaken by Microsoft themselves. A large number of modules have been written for Windows PowerShell over the years.
This book favors a PowerShell is PowerShell stance. There are differences between Windows PowerShell and PowerShell Core, but these details sit on the edge. Knowing how to use the help system, and how to explore objects, how to use PowerShell to meet an objective, is vital in either case.