Won't it all be in one long line?
> Typing \u001F or \u001E in some editors might be a faff, but it is hardly a showstopper.
Doesn't seem negligible when the editability issues with CSV were also minor.
> No escaping. If you want to put \u001F or \u001E in your data – tough you can’t. Use a different format.
Wanting those characters specifically is rare, but wanting to safely store an arbitrary unicode string - maybe a filename - is very common. Parsers might invent their own escaping to handle this.