Accept headers can negotiate extensions I suppose, but browsers can decide what they’d like to support, same as the rest of HTML standards. In the last decade,

Accept headers can negotiate extensions I suppose, but browsers can decide what they’d like to support, same as the rest of HTML standards. In the last decade, I’ve seen browsers drop content types (FTP) and adopt media formats (WebP). But no new publication formats. If my browser can render PDF, why shouldn’t it render Markdown?