We now support MathJax! Just go to your blog settings page under the Text Rendering section, and enable MathJax.
Forum discussion here: https://discuss.write.as/t/new-formatting-syntaxes/43/5
@write_as how will it federate? is it saved into the post as html?
@wakest Right now receiving platforms will just see the unstyled $equation$ syntax, so it'd be up to them to render it. Long-term goal is to have it rendered server-side and federated that way.