It appears that [XyJax](http://sonoisa.github.io/xyjax/xyjax.html) is developed independently from [MathJax](http://www.mathjax.org/). As a result, MathJax will not support nor test XyJax. This makes integration into MathOverflow difficult since we need to have reliable support for new features. We cannot implement such features without a suitable support plan from the XyJax developers.