Does Microsoft support Vulkan?
Microsoft has not expressed intent to support Vulkan. However, there are well defined mechanisms by which IHVs can ship a Vulkan driver on any version of Windows. But it will be as it is the case now with OpenGL. That is, it is up to the application to negotiate with the implementation to install an appropriate Vulkan driver for the hardware that is on the machine.
Vendors are enabled to ship drivers for whichever API they wish, and Vulkan drivers are already shipping from multiple hardware vendors for multiple versions of Windows.
Vulkan is available on all versions of Windows that are on DirectX 12, so there is potentially some value to the developer community to having a single API that spans multiple Windows versions.