Didn't LCC acquire DCA slots from DAL last year, in exchange for LGA slots? LCC/AMR could agree to give up a portion of said slots in DCA and be back to square one plus some extra slots and all of the AMR/LCC LGA slots.
I also feel they will lose a number of slots to satisfy the DOJ. Some small cities will be cut but then again DCA is a very constrained airport and when you can move 120 passengers as opposed to 50 passengers per flight, it becomes obvious that the larger cities will prevail and small cities will have to make a connection to reach DCA.