Well, it seems that capacity reduction is very likely or almost certain to be part of the mix of benefits pursued by this merger.
Regarding the East, there are many routes to capacity reduction large, small, more likely to inspire new entrants filling in the abandoned capacity and less likely to do so.
So, the decision will depend on how much contraction US/UA wishes to achieve internally and how much overall industry capacity reduction it would like to achieve.
The least of both would be to reduce IAD just enough to accommodate Fed concerns. Clearly, the Feds don't object to US's existing east coast network. UA could expand its east coast network by simply 'trading in' its east coast ops for US's east coast ops. Also, I think that UA could STAR-ify IAD, focusing on feeding Star Alliance partners going international out of IAD, but significantly reducing domestic hubbing.
However, I think that's not really the point of the merger now.
I think inducing the most capacity reduction by the industry is the goal.
So, I wonder if there might be a way to induce another carrier to re-align its east coast operations in a manner that does not grow net capacity on the east coast.
How this could be achieved without further consolidation say with Spirit, AirTran or even a three-way with CAL, I don't know. That's the problem with reducing capacity. No carrier has the ability to prevent others from expanding into the void.
Perhaps additional failures in the smaller carrier group would help reduce capacity on the east coast.
NK, B6, FL and WN's actions would be significant here. Could WN shift more capacity into the east? Could the others decide to start growing again? Or would the others shift their operations away from low-yield p2p operations to say, fill-in behind a newly vacant PHL market? Clearly, DCA would not spend much time under served.
WN would surely grow at either PHL or IAD should UA/US leave a vacuum, but by how much and what WN markets be reduced?
It's a chess game and UA and US are most likely to be mated. (pick your own meaning)