Haven't the airport stated that they are in discussions with CO to start a EWR service, hopefully in 2007 using transatlantic enabled 757 a/c? So DL serving JFK is possibly unlikely, unless they plan on a ATL route???
I think during 2007 we could possibly see the start of a US service, primarily to NYC. Zoom to YYZ is also quite likely, judging by the success of their routes from other regional UK airports. This developement is in addition to extra charter flights discussed already and the liklihood of new routes from the locos, with Jet2 ambitiously expanding and easyjet are due some extra services. Long lasting rumours regarding BE and FR could also resurface.
What the airport authority do need to consider, in my opinion is the lack of checkin and apron space at peak times of the day. Quite often all check in desks are occupied and parking stands are at a premium, especially with the growing number of based aircraft, which this summer stands at 26, not including the Emerald mail plane.