LaTeX? That's actually the primary use case I've seen for markdown -- to write papers/presentations/code notebooks in markdown that are then turned into LaTeX for typesetting.
https://en.wikipedia.org/wiki/X_Window_System#History I recall some pdfs of the Xeroc PARC showed more info on it.
Edit: I might have confused LaTex with https://en.wikipedia.org/wiki/NeXTSTEP. I think it was more efficient in handling data, but then again, platforms age whenever a new application needs more memory, so they got abandoned because it was more efficient to bundle it into something like Wayland...
Otherwise the Alto used Bravo and Gypsy for WYSIWYG typesetting: