d2 is a fairly new flowcharting language that is incredibly quick to write, and fairly easy to use. I'm not sure how easy or difficult it would be to implement this as an option, but I'd appreciate an alternative to Mermaid, if at all possible.
It looks interesting, but it would require some pretty drastic changes to installation and dependency handling. There are some features I’d like to add that would have similar requirements though, so I’ll keep my eye on its future development. :)