Maybe I could have explained this better since it's getting downvoted. Right now the two big modern graphics APIs are Metal (iOS / Mac) and Vulkan (Win / Linux / Android). These aren't the only ones, there are more for game consoles, UWP apps, etc, but they are arguably the most important ones.
Metal and Vulkan are not at the same level of abstraction. If you look up the code needed to draw a triangle on the screen (maybe the most basic graphics task), it is much, much more long and difficult to do it in Vulkan than Metal. Vulkan is a lower-level API. It gives engine developers more flexibility, at the cost of making basic things time-consuming and complicated.
OpenGL was the previous cross platform API. WebGL is almost identical to OpenGL. OpenGL still runs on Mac / iOS, but Apple has stopped supporting newer versions. The newer versions of OpenGL have closed the gap some with Vulkan and Metal (it won't catch up entirely, but it added some important features like compute shaders and it's easier to use it efficiently). OpenGL is still easier to use than Vulkan. The problem is the newer versions are not cross-platform, since Apple wants to focus on Metal.
Apple does not want to support Vulkan. Metal came out before Vulkan did, and it is a higher-level API. It's arguable if Apple should support it or not, but that's how it is. Microsoft also wants to focus on DirectX 12 (their API).
I was making the argument that a higher level API, Metal-style, would be a good base for the new web standard. Metal couldn't be used directly, at the very least it would have to be changed from Swift/Obj-C. But the idea of roughly basing it on Metal as mentioned in the article doesn't seem unreasonable, even Vulkan was based on a previous AMD technology called Mantle.
A low-level standard like Vulkan is hard to use directly, its adoption will depend mostly on people using frameworks / engines that use Vulkan. It's possible that due to its low-level nature there would be some performance advantage, although games using Metal also seem to get good performance on iOS. The disadvantage of Vulkan is that it is much harder to use than WebGL.
A fair amount of the WebGL content is not web specific. It is possible to write OpenGL content and compile it for desktop / mobile and the web. The most popular game engines, Unity and Unreal, both support compiling to the web and desktop from the same codebase.
In my view, there is no good replacement for OpenGL, now that new versions are not cross platform. Vulkan is much more work and does not work on Apple platforms, while Metal is easier but only works on Apple platforms. If they could provide a standard that is both easy and cross platform (by providing a C API library in addition to the web standard), it would provide the best of both worlds. The main downside is that it might leave some performance on the table compared to a low level API, and it would be yet another standard (which is why it would be important to provide a native library too, so developers have the choice of coding to only one API).