StrictMark breaks nothing. The arrow is one way: Markdown code mostly supports StrictMark. One may say that "mostly" is bad, but an arbitrary Markdown implement

StrictMark breaks nothing. The arrow is one way: Markdown code mostly supports StrictMark. One may say that "mostly" is bad, but an arbitrary Markdown implementation mostly supports an arbitrary Markdown document, so nothing new here. For ~full MarkDown support there is CommonMark code.