The standard in question is still "one of the standards" (and a "me too" one, "the one to end all the previous standards" (1) as far as I see it) not
the standard.
Remember claims of Flash being the necessary thing on the mobile web, and efficient too? It turned out it was never true.
Note there's still no web version of "pure" Vulkan. If it gets to be modified to be less "ridiculously low level" in its web variant, it is anyway going to come closer to the goal Apple proposes for the web.
Again, to quote from the Apples proposal: "We don’t expect this to become the actual API that ends up in the standard, and maybe not even the one that the Community Group decides to start with, but we think there is a lot of value in working code. Other browser engines have made their own similar prototypes. It will be exciting to collaborate with the community and come up with a great new technology for graphics."
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1) https://xkcd.com/927/