Markdown is very deficient in, say, organizing a blog post in several sections and subsections. There's formatting syntax, but not semantic syntax. No support for different styling at a higher level (in the template renderer); no support for generating indexes, footnotes.
(The state of footnotes on the web in 2014 is lamentable).
All these valiant efforts in having portable math typesetting that like to make puns with "LaTeX" fall regrettably short of enabling one to make a short blogpost detailing a mathematical curiosity, or even heavily-referenced semi-scholarly output. LaTeX is a template engine that happens to leverage a programmable typesetter. We have a programmable typesetter with modern JavaScript, can we focus on semantic templating already?