I do the same thing (markdown and mathjax) but I use TeXMe (https://github.com/susam/texme). I like TeXMe a lot because it turns any Markdown and LaTeX notes into a self-rendering file. Just open your Markdown+LaTeX notes in any browser and it renders itself beautifully, almost looks like a paper.

It is not wysiwyg though. But for me the convenience of distributing my Markdown+LaTeX source itself that can render in any browser without a separate compilation/processing step is a huge win!

See https://github.com/susam/texme#get-started if you are curious how it works.