Support syntax highligh rendered markdown, its currently only supported while editing the md file
While editing a markdown file online in VSO you can see that the syntax highlight works for the fenced block of code (see attached screen shoot).
however when you are done editing and the actual rendering of the markdown file is shown. the syntax highlighting disappears (see second attachement).
it is obvious syntax highlighting is possible for the language, both because it is doing it in the editing form, and because VSO can render other CSharp files with syntax highlighting.