Just because someone is going to link it, I might as well do it first: https://xkcd.com/927/

But yeah, "Too many implementations of Markdown" is not an issue a new markup language is going to solve.

"Markdown is slow!" is nonsensical: its implementations are slow (it seems the author tested this, but the link supposed to supply evidence doesn't -- I find it hard to believe that aren't fast implementations of Markdown, but perhaps). Nothing in the language makes it inherently slow.