Just some quick thoughts from the MathJax end.
* Elementary math is in our backlog. Even though it's not too hard to
implement, we just don't get enough requests for it to move its priority yp
(in particular not many serious requests).
* We would definitely want to implement TeX-like macros alongside the
implementation to facilitate authoring. Like Dani, we would prefer to align
that with existing TeX packages, but perhaps tools with TeX-like input
should lead the way here.
* David's \longdiv hack is available in the MathJax third-party extension
repository
https://github.com/mathjax/MathJax-third-party-extensions/tree/master/longdiv
.
* @David how usable is
https://code.google.com/p/web-xslt/source/browse/trunk/ctop/mml3mml2.js?
That might be easy to hack into a MathJax extension (like ctop.js) for
those interested in trying.
Peter.