I worked on a database whose format was derived from Pick [1], that used 0xFE, 0xFD, 0xFC as record, field, sub-field separators - which was great until we had customers that needed those code-points for their data (i.e. in needing to enter data that was not all in English) and we had no escape mechanism. Using characters from the control set would have made so much more sense.

[1] https://en.wikipedia.org/wiki/Pick_operating_system