Your extension idea sounds similar to this that was posted yesterday:

Pikchr: Documentation https://pikchr.org/home/doc/trunk/homepage.md

Pikchr – PIC-like markup language for diagrams in technical documentation | Hacker News https://news.ycombinator.com/item?id=24601971

I don't know if you're referring to Go or GraphViz as the extra dependency (or both). It looks like Pikchr doesn't have any external dependencies, it's just a C library.