Ask HN: Canonical form for blog content?

Suppose you want one canonical form for all your blog content. I assume it would be a variant of markdown.

However, you want to preserve tags, table of contents etc.

And you want to be able to submit this content to a static site engine (Jekyll etc), or the major private platforms (say, Wordpress, Medium, Ghost) and also the closed garden blogs (Linkedin).

What would be the best form and structure to store them in? One folder with all the posts? How would the meta-data be stored?

If that is not possible, is it possible to have one target (say Wordpress) which makes it easy to export to others?