I hope DL isn't stupid enough to hop on the JFK-LHR run. The last thing we need is another carrier to bring down EVERYONE's loads across the board
If you really believe THAT, then I have a bridge to sell you!
JFK-LHR is infamous for it's high-yielding O&D. And since when did USA (and an increasing amount of Euro-airlines) believe in allowing the competition to flourish for the sake of yield preservation? Last I checked... never! Witness NYC-LAX, NYC-MIA, NYC-BOS/WAS, etc.