The particular implementation I was speaking of was for internal wiring inside a mixing console I was building. For module-to-module connection, this was a space saving and inexpensive solution. The balancing was done with transformers, so there actually was no ground reference. As I mentioned before, I was using shoulder washers with the RCAs so that no contact was made to the chassis at either end.

I'm not suggesting using RCAs routinely for balanced connections, but just that I have used them in equipment with good results when the use of other types of connectors didn't make sense.

Electrons don't know or care what type of connector they're flowing though as long as that connector is otherwise suitable.