SMI/J already telegraphed the future of DC.
http://www.flightglobal.com/news/art...dulles-393395/
IAD is too expensive (landing/boarding fees), has an outdated UA terminal, and only will get MORE expensive with a new terminal C.
Many flyers prefer DCA for domestic travel, and DCA is cheaper, making IAD domestic flights hard to compete.
The future of IAD is for select international routes that command premium airfares (NRT, DXB, European capitals, etc) and just enough domestic feed to fill the seats the O/D travel does not fill.