It seems like a very smart move from Microsoft. They get rid of the abysmal performance of windows's file system and spawning new processes by using... linux! Provide also an excellent terminal so that developers have the best experience with command line tools, all this without leaving the convenience of Windows!
Not surprising since they dominate the desktop market since forever being smart at strategy.
The only weak point of WSL 2 to my point of view is that you say goodbye to development of native Windows application because you are effectively on Linux. It means you either setup cross-compilation which can be annoying either you go with Visual Studio, the old MS way.
For the moment I will stay with MSYS2 plus Mingw64, they are both excellent and provide a good experience to develop native applications on Windows. At home I will keep using Ubuntu, of course.
For the introduction of WSL 2, I think many of the people using Mac OS X may switch to Windows. They never fully embraced the free-software philosophy and chose Mac OS X because of the high-quality hardware and software and the good terminal experience with unix-like environment. They will easily switch to Windows now.
The small group of people using Linux will probably stay on Linux because of dislike for Microsoft practices and the fondness for free software.
Bad news for free software, good news for Microsoft shareholders!