Have there been any discussion of extending markdown with support for link relation types?
That would allow you to give meaning to the links. Which in turn can allow HTML representations and a user agent to do things like expose navigation for links with relation type next, prev, up, etc. Or possibly things like import of another markdown file into the current one. It could also use any link with relation stylesheet to be included as a style sheet in the resulting HTML.
An early suggestion would be syntax like this:
[link](/url "title" "stylesheet") or [Link](http://a.com)[rel=stylesheet] It could also support future possible link params, for instance: [Link](http://a.com)[rel=stylesheet][target=_blank]