You've misunderstood what this is. It is a full kernel for the Linux subsystem, which provides the ability to run Linux code in Windows. As I understand it, the existing solution maps Linux kernel calls to the Windows kernel. I can imagine it would be much easier to just provide a true Linux kernel rather than try to support a brittle mapping layer.
They are not putting in a Linux kernel for Windows. Huge difference.
They are not putting in a Linux kernel for Windows. Huge difference.