USVs are easy to edit in a text editor

I don't see how that's the case.

If a format with sane separators was common, so would editors that could edit that format be

Sure, but that's a hypothetical future editor, not something that currently exists.

Edit to add: I also disagree with "sane" in that context. New separators won't solve anything. You'll always need escaping/encoding/encapsulation; get that right and everything else follows. JSON is comma-separated and does just fine.