still, DL is operating 15 flts/day just on JFK-LAX and SFO; the fleet would be highly stretched to make it the only aircraft on those two routes.
Given that JFK-SEA is a key feeder flight for flights to Asia, the chances that it will not have any BE seating is slim.
Even if you are looking at schedules today, they can change as little as 45 days before departure and since the 757 and 763 all share the same types, DL can make equipment swaps as close as the day of departure with little impact to the operation.
Again, there is no evidence that DL is removing widebodies from the JFK-LAX route where it currently operates 5/day. DL could reduce that number but DL is filling the aircraft to the same levels it has done in the past, has managed to increase yield even with the current number of 767s, and is carrying tens of thousands of pounds of cargo and mail which they weren't before.
And, yes, the plan all along has been for several of the 767-300ERs to replace the retiring 76Qs, not only for Hawaii flying but because DL cannot get rid of its 767s at LAX without having more gates to be able to maintain the number of seats via more frequencies. The 767s are the only aircraft that can carry 250 passengers and still operate cost efficiently without taking aircraft that could otherwise be used for int'l ops.