I would have expected this to export CommonMark, but it seems like it's not quite up to that yet. Is that on the board for a future release?

This isn't to say I prefer CM -- because Markdown came into being from Gruber's script. In a literal sense, "Markdown" is defined as whatever `markdown.pl` is, warts and all -- however, contact with the outside world forced things to move in a direction that is (so to speak) more organized that what John originally wrote.