[cxr]

> The next question is, how would you get the second layer of github flavored markdown fluff (latex, mermaid, etc), that is generally not standardized, to be supported in browsers as well?

Don't. GFM should stand for "GitHub Flavored Markup", since that's how people treat it—yet another markup language, which they find more convenient than other markup languages. The "Markdown" as it is used on GitHub and the people who author it abandoned the premise. Markdown was intentionally designed so that the "raw" form of a given Markdown document is supposed to be a valid way for humans to consume it. That's not how Markdown is used on GitHub, however; no one pays any attention to the readability of the raw form. It's just another input for their compile-to-Web pipelines to suck in (or for github.com to render as substitute for a project landing page).