I would be very careful with adding complicated types of content. We already have the mess with HTML mails which can be a attack vector and track the user.
When I see Signal there is no markup and style, only plain text. Sometimes I which that I would have simple styles like bold etc…
So I am not totally against this but I think developers should be very very careful about this and don’t add to complicated stuff that’s hard to validate.
I can’t judge how complicated TeX is. Isn’t there another way for math notation like Unicode characters or so?