The POSIX spec defines portable and non-portable ASCII characters, prudently placing the separators in the non-portable set. In order to nest tables, base64 (or whatever portable encoding) code the table into the field. This works much better, easier and more error-free than any escaping strategy.

Regarding visibility in editors, if you are nesting tables I don't think you care too much about manual editing, but if you do, it is easy to setup vim/emacs/vscode to display the ASCII separators. I am being told even notepad++ can display those, there are no excuses.