Super User kinda already does this, the second most popular tag is Windows 7, then Windows, and Windows 10 is up there as well.
If you look at the Windows tags, they all have at least 200 questions, so it's well established.
I disagree. 200 questions is not a lot, and Windows could easily have it's own SE with thousands and thousands of questions asked each year. Just like the Mac SE called "ask different", which is about other Apple products too, but the most significant is probably the Mac.