Laudable, but I don't think TapirMD will gain much traction.
First, your landing page doesn't describe how TapirMD fits into the Markdown universe. I just see a list of features. Why should I read the list? Ah, the spec page[0] has some info, but it should really be on the landing page.
Second, and more importantly, TapirMD is not a superset of CommonMark[1]. GitHub had its own flavor of MD, but it's been some years now since they migrated to a CommonMark base plus extensions[2].
I recommend looking more closely at the CommonMark universe and innovating there.
[0] https://tmd.tapirgames.com/specification.html [1] https://commonmark.org/ [2] https://github.github.com/gfm/