Why would it matter if it's upstream? Upstreaming something like this is not really useful to anyone but Microsoft; it is still something that is inextricably tied to Windows and WSL.
The point is not "extinguishing" Linux per se, it's achieving enough lock-in that only Linux that Microsoft customers can use is WSL.
WSL is not a Linux. It is a Windows subsystem for running Linux userlands. (Almost as if the WSL name isn't totally nonsense!)
The "default" is Ubuntu. But Debian is supported, OpenSUSE is supported, Kali is supported. Unsupported but available, you can get Alpine, CentOS, Fedora, Arch, lots of distros.
That was WSL1, WSL2 is a micro-vm running the Linux kernel and whatever userland you want. Ubuntu is just the most advertised one, but all are equally unsupported by MSFT, support is provided by the distro "vendor"
By "supported" I mean "available in the Windows Store." I believe that those are submitted by the distro vendors themselves.
And from a lock-in perspective, the userland is all that matters, yeah? If an app runs on Ubuntu, whether it's WSL 2 or in Docker or in a a VM or on bare metal. If it's all the same, then it's not a Microsoft Linux, it's just Ubuntu. Or whatever Linux you want.
You could say that WSL is not a GNU/Linux. But since WSL comes with its own kernel, part of it is definitely a Microsoft-extended flavor of the Linux kernel.
Even if this driver went upstream, it wouldn't be any less tied to the WSL virtualization platform.
The only part they're upstreaming is some ioctls to send opaque blobs from closed-source binaries on the Linux side to closed-source binaries on the Windows side.
Well, they have so far: 1) embraced Linux. 2) extended it with proprietary functionality (Windows living outside WSL), and now what is next?
How is this not the same?
Of course, the MS employee will downvote me automatically, the VS code users will downvote me too, and I will lose 5 karma for saying the truth.