The Solution is 787
The issue DL has is it needs a smaller more fuel efficient plane to fly those routes. NW ordered the 787 with overflying NRT in mind. I hear that directly from a number of PMNW folks on the 787 program. There's a premium for the NonStop, the loads are easier to manage than a 747 or 777, and the plane has the range for TPAC missions.
DL could do a JFK-NRT, but it's a long mission that only a subset of their WB fleet could do and it could be a blood bath if it turns into a fare war.