Is it likely that the Feds would allow a super-domination of DCA by the new AA? I doubt it; I think for this final merger they're going to be looking to avoid "Superhubs" and an AA/US combo at DCA, without any givebacks, would certainly qualify.

If it were three or four years later, when the Metro (finally!) extends to IAD, might be a different story.

I think it more likely we'll see increases in UA frequency at DCA in the short run. Once the Metro is in place, could be an entirely different story.