[CJefferson]

While MathJax is great, the biggest problem is that 'TeX' is a very poorly (read undefined) standard, and it's fairly easy to produce things which TeX renders fine, but MathJax and Katex both bork on.

Of course, writing a clean "standard" which covers most of what people expect when they say "TeX", and implementing that, would hopefully produce the best of both worlds.