Again reimplementing Emacs Org mode. Nice work! This looks terrific, but honestly Markdown is a document markup language. Org mode, while superficially similar in scope, is actually a data storage and exchange format. The data manipulation and querying built around Org mode are unlikely to be replicated in Markdown.
I really want to like Org mode, but I just can't. The syntax feels too out of place. With markdown it's just a few extra symbols, but using Org mode feels like writing LaTeX in a way.
Same thing with MediaWiki - I love the wiki system but WikiText is just so bad.