There is actually an ASCII character that doesn't appear in strings, and is meant to be used as such a separator. Actually two of them, record (30) and unit separator (31).
Sadly, eventually someone will want to enter one document as a field in another document and then you end up needing escaping anyways. Using a rare symbol for the delimiter would still be nice for typing documents by hand, but it would have to be available on modern keyboards to be convenient.