Blargh. It annoys me that MathML was even a thing. We've already had a perfectly-fine and widely-used markup language for mathematical formulae; it's called TeX. Ideally, I'd prefer that HTML5 include a tag, or something similar, that takes TeX as input and produces formatted output. A side benefit would mean that every browser, and every system, in the world would have TeX installed! At least MathJax can take TeX as…
Having a context-free representation is IMHO a necessity for processing untrusted inputs (e.g. webpages). It also makes it a way faster.