I actually wonder if some kind of #JavaScript polyfill could be created to implement support for these features without UA support. It would be suboptimal, similarly to how #MathJax is inferior to UA support for #MathML, but could work as a stopgap solution to promote the adoption and standardization of these extensions.
TeX Commands available in MathJax
https://www.onemathematicalcat.org/MathJaxDocumentation/TeXSyntax.htm#symbols
#MathJax_torture #LaTex #TeX #MathJax