I wish Asciidoc was more popular
Very briefly on admonitions: there is nothing stopping you from adding them to markdown yourself:    
    You _really_ shouldn’t
    play with matches, Debbie.
    

Later on in that document:    
    warning {
        display: block;
        color: red;
    }
    

Which is a very long winded way of saying that you can use markdown for authoring actual content, and then use good old HTML for styling whatever else you want to.Relying on asciidoc for styling elements like admonitions always felt like the wrong tool for the job.  Like writing a Java generator in Perl, instead of just writing actual Java.