This answer states that MathJax in comments on Android is disabled by design: https://meta.stackexchange.com/a/251465/177540
To me, "by design" means how you'd like it to work (i.e without bugs). The only explanation I've seen is "technical difficulties", indicating a bug. Since you can render the MathJax on demand via a hidden menu item, what's the difficulty? Are we likely to see MathJax in comments any time soon?