Quarkdown is a step in the right direction. One step closer to HTML.

Tough call. I think Markdown is not an authoring tool at all. In fact if you read through the changelog of GitHub Markdown, you will read a very detailed critique of the shortcomings of MD.

It isn’t a specification. This is MD’s biggest weakness as well as strength.

## can be a subheading or heading level 2.

How about an empty line between paragraphs or after headlines?

After reading this I consider MD an idea. A fantastic idea but not a spec.