I think the way forward here with math and other niche document formats (like MusicXML) is to keep them out of the HTML standards and let people create web component libraries that handle rendering.
As a practical matter this will bring implementations to all browsers much faster than waiting for four large organizations to decide that a format is important and allocate resources. Even better is the real-world experience those libraries will gather so that maybe we get something better than what a committee would have designed in isolation.
For mat specifically, TeX really seems like a better way to go for now. I wrapped KaTeX in a web component so that it's easy to use in HTML: https://github.com/justinfagnani/katex-elements
As a practical matter this will bring implementations to all browsers much faster than waiting for four large organizations to decide that a format is important and allocate resources. Even better is the real-world experience those libraries will gather so that maybe we get something better than what a committee would have designed in isolation.
For mat specifically, TeX really seems like a better way to go for now. I wrapped KaTeX in a web component so that it's easy to use in HTML: https://github.com/justinfagnani/katex-elements
You use it like:
I imagine the equivalent for music will be better than MusicXML