Well, provided that you are tied to msys and you can never ever compile guile with a microsoft compiler, that is ok. You are talking only about your use case. The reality is quite different: if you want windows adoption, you need to use the native toolchain to compile. I have extensive experience with cmake and autotools and quite a bit with meson already. I can say with confidence that keeping autotools and taking windows seriously at the same time is just impossible. So my view here is that to have a decent windows port we would need native windows threads and compile with microsoft compiler (that is why I would be proposing meson). You just have to see the gstreamer guys experience when switching to meson and the huge improvement it was, especially in windows.