Appx and UWP are more packaging (like rpm, deb, msi) formats than an executable format. PE is behind everything in windows and the amount of effort required to change that seems truly Herculean, even for an organization the size of Microsoft. Heck, even executables for windows ARM were PE (as well as UEFI binaries). But even if you assume that they do go forward with something that insane, if they want developers to write software for it, they’ll have to publish the format specs so that gcc and llvm can implement them so that the tens of thousands of existing libraries could be ported

Yeah but given that dxvk is a thing, a switch to dx13 would just need to be implemented there. The underlying wine layer would only need to change if the PE format changed. But even then, that would destroy backwards compatibility in the windows world… something that Microsoft’s enterprise customers would (rightfully) crucify them for.