I think you'll find it hard to do. Markdown was designed for web and it won't be an easy task to handle all of its quirks with no HTML-capable viewer. Not saying it's impossible, just saying it'll be hard.
Rather than a datatype, I'd start with a MUI application for displaying markdown and a custom MUI class to draw it. You will likely want to use Cairo to render text / images / etc since that'll let you use full Unicode.
I'd also recommend using ObjectiveC-MUI for all this since that's the quickest way to get started and removes a lot of boilerplate.
