Country? Maybe. If PLJ's billing drops enough to where a country station would probably pull in similar numbers, I could see Citadel going for it, but very low maintenance...few or no jocks, on the cheap.
Real oldies? No way. 50s and 60s isn't going to cut it in NYC, from a billing standpoint...they might as well just stick with PLJ and play fourth fiddle behind Lite, CBS-FM and Fresh.
Standards? Absolutely no way.
CHR? Would be a great idea to take on Z100 (and to a lesser extent, KTU, Hot 97, Power...even Pulse!) but that kind of format would require a big investment to run...it would not be cheap, and I think Citadel is looking for cheap at this point.
As for Rocky Allen...his type of programming would fit in with CBS-FM's target demo, however, as much as CBS-FM is still a station where personalities have somewhat of a prominent presence (by 2008 standards)...I still think the music there is king, and the type of show that Rocky does wouldn't fit into the format.
If 95.5 went country, maybe they could pick him up for mornings and voicetrack the rest of the day. He probably would also fit in nicely on NJ 101.5, but that station's lineup doesn't seem to be changing anytime soon.