Syndex rules would generally keep it from happening nowadays, duopolies notwithstanding. Though another exception seems to be for rimshot stations on the edge of a bigger market, where the town is kind of in the middle of nowhere but not big enough to have a full complement of network affiliates—i.e., WFLI/Lafayette, IN or WHIZ/Zanesville, OH.
I remember a few years ago (2010 or thereabout), being in a hotel in Lafayette on business, and seeing Wheel playing at the same time on both WFLI and WTHR (Indianapolis). I know that’s probably not exactly where you were going with this topic, but I thought it was a semi-relevant point.