Re: What are the benefits?
Try rolling out Linux in a company of business people and you'll get the advantage..
I am not really that much of a Microsoft fan at all but I was using WSL pretty much from the start and I have to say it's pretty good. I am sorry for RMS to see GNU core utils getting used within windows. But damn it's convenient.
The bigger picture is of course that Microsoft has already started to pivot everything into the cloud. I can even imagine Windows will be more of a "software providing center" with stuff like MS Office, Visual Studio or even the Windows GUI running as proprietory "Microservices" on a Linux Kernel. It's basically what has been done for decades by Apple with their BSD-based OS.
At the end of the day - does 95% of the user actually care about which system calls are made and the details of the way threading works? If Microsoft keeps the "Look and Feel" and successfully integrate it with the Linux ecosystem (where Microsoft has become pretty active lately) they con only win.