You can run things like VcXsrv or Xming, then you can pretty much run anything through them, including window managers. When WSL went mainline I had all sorts of fun playing with it, building Servo and VLC and running them in a tiling wm, just because I could. (Not exactly productive time though)
And I can't seem to edit my post, but your comment about it be a Cygwin replacement is spot on. It's definitely replaced the need for it almost entirely.
