Airtran is getting more DCA slots, and it's entirely likely that LUV will come into DCA with the F9 deal. Now, that becomes interesting--F9 has the goldmine "beyond perimeter" slots. And a gate. That won't help LUV _inside_ the perimeter without finding more slots.
F9 has 3 "beyond perimeter" slots but they do not hav a gate or ticket counter space. They are leased by USAirways. WN might wind up selling the DCA slots to either UA or US since they don't ever fly to a city with only 3 flights. And they have no way to expand flights to DCA.