I've used mermaid from within markdown before, but the whole premise still leaves me conflicted. The original selling point of markdown is that it wasn't a markup language; it was readable text that could optionally be rendered with some extra niceties if you were reading it in something more sophisticated than a simple text field. While mermaid is undoubtedly useful as a textual language for describing graphs, the spirit of markdown would favor something that actually looked like a graph without needing to run it through a renderer, something more akin to ascii art, but with well-defined semantics such that it would produce something reasonable if you did have a renderer at hand.