He created something that got popular (and which was derivative itself, in the first place, but anyway), and when people try to standardize and fix its flaws, he objects.
Any decent, non-prick, person in the tech world that I know of would be happy and flattered to have his 10+ years neglected project be improved, standardized and fixed, and either he would get involved in the process, or say "sorry guys, I don't have time, but I wish you all the luck".
This prima-donna behavior means he should be left out for any future discussion regarding Markdown and ignored.