I believe in a situation like that, it might get grandfathered in. However, I would have a hard time seeing an independent or a netlet owned by a company with an ABC, NBC, CBS, or Fox affiliation (or owned by the network themselves) get high enough ratings to bump a major network station down position #5 and lower. If the duopoly is owned by the networks themselves, there's no way they want the other station to outperform the major network station.