asciidoc support would require an ansciidoc renderer written in javascript, which does seem to exist[1](although I haven't used it). This also highlights some of the problems with markdown because it is an insufficiently rich language for generating semantically meaningful markup for use-cases beyond blogging. There has been some really interesting work on "scholarly markdown"[2][3], but given the social and technical complexities of markdown implementations and the community[4] seems like adding asciidoc is easier than fixing markdown.