In ideal world, but it's too late. The codebase is old. It's very difficult to backport/reimplement/integrate features (tons of APIs, kernel features, etc) that new software relies on. Also, because of compatibility you can't remove all the mess.
I would even say that from the usability perspective, Windows 2000 beats them all, but quite some useful APIs were added in XP and 7, including better Unicode support, driver signing, UAC. But 10 and 11 were just a waste of effort.
WSL2 is just a virtual machine. Hyper-V was first shipped in Windows 8, which is not too far from Windows. But things are even more bright. Qemu already had the "kqemu", which what eventually became KVM when merged into the Linux kernel, and it worked _even on windows NT 4_, and if course it worked on 2000 and XP.
So porting Hyper-V/WSL2 as a driver onto Windows 7 should be even less of a problem than WSL1.