[indentit]

I guess these days it is better to compare GitHub Formatted Markdown, a common extension to CommonMark, as opposed to plain CommonMark. It supports code blocks with language hints, tables etc. Also, I am pretty sure Markdown with metadata (sometimes referred to as "front matter") already exists and is called MultiMarkdown, though presumably not as powerful/useful as what you describe here.

[gnomewascool]

> code blocks with language hints

CommonMark also supports code blocks with language hints (using the ```lang... syntax). What Org-mode has, in addition to code blocks with language hints, is inline code with language hints, which neither CommonMark nor GFM support.

> tables

I'm horrified that, indeed, CommonMark doesn't have tables, though you're right that most people now just use GFM.