Your point about the possibility of unevenly sized text and line breaks mucking up the whole layout makes sense. I wasn't thinking about that. I think a better-than-nothing solution would include the stripping out of markdown formatting that alters the rendering in, image references (I'm new here, are images even allowed in post body content?), and converting the markdown URLs as you mentioned.
Another thing that could influence what people put in there would be some example text in maybe some helpful guidelines alongside the post form.
Looks like at least I've got a few more reasons to finally sit down and pick up a little Rust.
Well, here's a thing I didn't know about before that might be useful to you – a tool to extract the dated from the *.crd files.
https://github.com/sbechet/crdextractor