Playstation, Mac OS and many others are based on BSD for that reason (and probably other reasons as well).

I cannot imagine a BSD-based MS Windows but it would be cool!

This would probably solve slow filesystem I/O (which is one of the major pain points for me when working under Windows, especially if you have a large number of small files).

However, it's important for Windows to keep backward compatibility for applications using old APIs. I think that's a major selling point vs. other platforms.