I had wanted to find a source syntax I could add to Markdown so that when it was rendered to HTML, it would include RDFa stuff in it. I'm not sure that's worth the effort, but I started it here.
My next thought is to use HTML comments to hide Turtle statements in Markdown source, and maybe write some code to add to RDFlib that knows how to navigate a Github repository to find the *.md files, go to their raw source files, and extract a semantic net based on that. So that's my next idea.