CBS-FM did run jockless all day for quite a while. It was called Jack FM. We know how that worked out.
Yeah, it significantly increased the 25-54 demos of the station over the oldies format.
They only changed to classic hits (not oldies) because they were party to the early PPM tests in Philadelphia and saw how much better a more 70's based format could do once the PPM went currency.
"Jockless" is not the same as automated with voice tracking.