You only have to look at the routes which have two 747 departures within an hour of each other
Such as HKG-LHR, JNB-LHR and SYD-LHR which I admit are contenders, but on the JFK you also have to think about the logistics of getting 500 passengers on board, back off board, and getting their baggage to them in a reasonable time. The great masses looking for the cheapest fare may put up with all that, but on a route such as JFK the business passengers are looking for quick check-in, fast boarding and the same at the other end, that is why concorde was successful, in that it saved time.
I can't see a 500 seater being able to give that punctuality, but time will tell.