Using the slots for more feeder traffic into DLH's European hubs is an interesting idea, but probably not the answer except on a very limited scale; Lufty have enough slots in their own right to be able to do that anyway. Increase in passenger numbers can probably be better achieved by replacing CRJs and 737s with 319-321s.
Given the success of the midhaul network, further expansion to suit the needs of the oil industry, and to integrate travel between the centres of that industry, seems more likely.
Of course, I am still only speculating!