Markup languages should support TUI / plain terminal, because many people still use that as their IDE. If I can’t pipe a file around to standard *nix tooling, it’s not a good format.
You can pipe a file with unicode control characters. If your terminal supports Unicode (it must), it can even display those control characters (e.g. as small curly braces) or choose another form of presenting the text. Markup languages do not have to support every legacy terminal - all new tech requires users to upgrade at some point.
