You may not understand how important Microsoft considers backwards compatibility. Switching to a Linux kernel would eliminate all of that, and that is simply not an option for Microsoft.
The Linux kernel is missing a lot of esoteric things that the NT kernel has and that people use a lot, as well.
Windows as we use the word today (any variant) will not ever switch to a Linux kernel.
I do hope one day that Microsoft put a proper GUI on Linux though, no X, no Wayland, but something smarter and better than those. Probably also not likely to happen but I’d love to see it if they could do it well.