Looks interesting. Cross-references within the same doc are surprisingly rare in Markdown editors. However, there is no import function for existing Markdown (or any other file format)? That makes it pretty hard to try this out in a serious way.
To have some content, open any website and press cmd+a, just past it into the editor. depending on the size it might take a little but the editor tries to clean up your pasted content and inserts it.