I like the idea of using markdown to take you as far as it will go, and then having a function system to handle the edges and a mode system to switch to maths mode.
I’ve long left the field where I need to have precise reproduction of layout for large volumes of text, and haven’t touched LaTeX since the early 2000s. But it sounds like it’s currently doing most of the right things, has the support it needs, and most importantly, has institutional support.
Also sounds like it could be scripted to take my reams of markdown text and convert it to a stable layout format; I remember trying to script that for LaTeX with Perl’s mod:latex in the 90s, and eventually realizing I’d be better off to just re-type it.