The lack of a consistent standard for Markdown is a big obstacle for this. Markdown comes in various "flavors" so you end up with a quirks mode nightmare as bad as IE6-era HTML, if not worse, and you sacrifice expressiveness as part of the bargain.

Hopefully the industry will continue standardizing on Commonmark. Maybe it should have its own media type?

    Accept: text/commonmark,text/markdown,text/plain

If you go by RFC-7763 and RFC-7764, then CommonMark would be served as:

    text/markdown;variant=CommonMark

I didn't know about "variant=", thanks.

Potentially unpopular opinion, but GitHub flavored marked down is almost inarguably the de facto standard, and the vast majority of markdown in existence is GitHub flavored. We should just embrace this.

Commonmark is pretty close to 1:1 compatible with Github Markdown as far as I know. And Commonmark literally is a standard with a spec.

If we were going to really push this as a standard, this would make a lot of sense.

That’s a simpler solution in the sense that there aren’t many steps to get there from existing tools, but the HTTP protocol is incredibly complicated compared to Gemini, and Markdown is complicated compared to Gemini’s rich text format too.