Would it be possible to enter equations into comments and have them rendered with MathJax (both in MetaPDF and the exported HTML annotations)?
I'm thinking something similar to how RMarkdown incorporates the ability to write LateX equations.
+1 for markdown + math support
In the mean time, you can use the chrome extension "TeX All the Things" to achieve this. The extensions is a little weird though because it will sometimes renders normal text on the webpage as math.