I guess I'm directing this to the guys who work the busy airports (not necessarily JFK, but those where you might find GA). Do you guys know that most are going to be operating IFR and can do without the "IFR to..." or "clearance to..."?
Well, as we all know, all commercial flights are IFR, so that eliminates a lot. Most of those pilots tend to make it short and sweet, like "Clearance, Cactus 456 going to Charlotte with November" to even shorter, like "Southwest 405, Omaha, Alpha", and that's it.
GA... it depends, and I'd say on location more than anything. When I went down to KLAS and listened in, they could have gone either way, but most of them being IFR. Those that were VFR just wanted clearance out of Class B Airspace, while the bulk of them avoided KLAS altogether, opting for flights into KVGT and KHND So it really all depends on what smaller fields their are that can feed off the main arrivals into the big fields. Example: KTEB and KCDW for the JFK/LGA/EWR in the New York area.
But in smaller places, like OKC or OMA or others in the Midwest USA, you may see a that ratio evened out, where half is IFR, and the other VFR.