Seriously, the moment there's a linux distro that really "just works", even with games on NVidia cards, I think Windows will lose a very large chunk of market share. So many people are sick of it, but most people still fear that stuff won't work right on Linux.
Anyway, Valve is probably the most likely party to pull that off.
Why, though? If the Windows subsystem for Linux can provide many people an adequate environment for dev work, why can't the equivalent Linux subsystem for Windows provide an adequate gaming platform?
Even Microsoft learnt that with WSL, hence why WSL 2.0 is a plain VM, hardly any different from Virtual Box or VMware Workstation, other than is already on the box and doesn't cost extra.
Anyway, Valve is probably the most likely party to pull that off.