[om2]

As it happens, OpenGL was so high level that supporting it on top of DirectX was feasible. A number of Windows browsers use the DirectX back end to ANGLE, so users don't have to download OpenGL drives.

Unfortunately, that doesn't work as well for Vulkan. Vulkan is the lowest-level of the three APIs, so it's hard to support on top of Metal or DirectX 12.

[modeless]

Since WebGL was released, Microsoft has demonstrated a new willingness to support Web graphics. They joined Khronos, and now ship a WebGL implementation of their own with Windows. I have confidence that if the industry moved toward a WebVulkan standard that this new Microsoft would make platform changes to better support it. Unfortunately I have no such confidence about Apple.

[om2]

Why don't you ask Microsoft what they think about this proposal instead of speculating?

[MrScruff]

Shipping WebGL is not the same as shipping OpenGL support, which they don't do. WebGL on Windows browsers is built on DirectX. Apple ship a WebGL enabled browser.