Joplin is a nice tool for notes that contain images, tables or lists, but sometimes you have data you want to represent as a graph.
Hence it would be nice, if Joplin would support dot graphs.
The nicest integration would be inline graphs for markdown files.
Since this might be complicated, I would already see support for dot files (the whole note is treated as dot file and displayed as such) as a big improvement.
I looked around a bit and found a really nice JavaScript editor (but i have no idea how to integrate it or how much work this would be):
https://edotor.net/