I've seen this pop up a few other places in the ecosystem already, defined as:
content: {
"$type": "site.standard.content.markdown",
"text": string,
"version": "1.0"
},
I think it would be good to have an explicit markdown type built in for content.
there are already community initiatives for this content type you might want to take a look at: https://markpub.at/
we have been going back and forth on this. its hard to add content types as we don't want to dictate content types. but we have had requests for this so much that we may implement it. but we have to think through the best implementation for this.
i am partial to the weaver implementation of a markdown content type too. the best way to showcase good lexicon design is through iterating and building an actively used lexicon. weaver has been refining their markdown based lexicon for a bit.