WCBS-FM New York is currently running an HD4 channel, but the audio is a duplicate of its HD3, CBS Sports Radio. Maybe they're planning to put something else on it soon.
WWFS New York was running foreign language programming on an HD4 channel, feeding a translator somewhere I believe. That's now been discontinued and I think the programmer leased an HD2 channel on another station, maybe WNSH HD2.
Speaking of WHSH New York (actually New Jersey), they were running religious programming on an HD4 channel feeding area translators. Not sure if they're still carrying it as it's hard for me to get a lock on their HD signal.
WVIP New Rochelle, NY is using an HD4 channel to feed Soft AC “101.5 The Breeze” to translator W268AN in Planinview, Long Island.