LaTeX/Mathjax support
Element web recently added support for rendering LaTeX equations in messages (currently only as an option in the devel version). See https://github.com/vector-im/element-web/issues/1945 for details.
The core idea is that if the sender supports it, LaTeX equations will be encapsulated in a code block in a span with a dedicated attribute for the LaTeX source. If the client supports it, this is then formatted using mathjax.
Fractal could use the LaTeX parser from latex2mathml to check the syntax and get a more convenient data structure to work with. Rendering would then probably require some extra work.