But maybe that's insufficient. Hugo[2], one of the most widespread static site generators in existence, supports Pandoc markdown flavors as well as general GFM.[3]
They are not supported by GitHub’s GFM, and you are being incredibly bad faith about this fact.
If you are comfortable calling Markdown a futile exercise in avoiding proprietary control of a universal, simple document format for wide interoperability across natural languages, programming languages, and monopoly interests, then you and I are Microsoft vs Sun over Java in the 1990s.
The original Gruber-Shwartz format, which is in fact fundamentally a perl program attached to a brief expression of its intention, is not used by anyone except those who still use the perl program. Every other implementation avoids thousands of corner cases present in the perl, while of course producing its own.
If you are comfortable calling Markdown a futile exercise in avoiding proprietary control of a universal, simple document format for wide interoperability across natural languages, programming languages, and monopoly interests, then you and I are Microsoft vs Sun over Java in the 1990s.