The following steemit post:
also discusses this issue. Looks like there was a feature request for mathjax in steemit:
https://github.com/steemit/condenser/issues/7
I wonder how stackexchange dealt with the security issues that led this feature request to be closed?
I wonder how hard it would be to fork the UI:
https://github.com/steemit/condenser
and try implementing this?