If there's not enough file system performance, they should improve their file system layer. It'll benefit all Windows applications as a side-effect. Believe it or not, but people actually use Git with Windows :) If Linux is able to pull much better file system performance, I don't believe that it's just impossible for Windows to achieve similar levels.
I think that Microsoft sent many patches to Linux kernel before. It might look weird, but it's nothing really new. Their Azure business uses Linux.
Also, while I think it is useful. I imagine much of the hype here is also from the weirdness of it all. Would you agree that it is noteworthy that Microsoft is publishing a Linux-kernel for Windows? It think it is.