BWI: No longer a low cost airport?

     When I search for flights I have always used Kayak for finding the best fares.  I also search on Southwest as they don't usually show up in the other airfare search engines. Southwest is supposed to be a low cost carrier but it has never been that for me.  It seems like the two carriers that have the best price for flights from BWI have been USAir and Airtran.  Of course this can depend on the city to which I am travelling but I probably use one of these two carriers 75% of the time.
     So what is going to happen as these two airlines merge?  The Airtran flight checkin has already been moved to the Southwest terminal as these two airlines move to merging. When you go to BWI the Southwest terminal is always crowded and the rest of the airport can look deserted. 75% of the flights from BWI go through the Southwest terminal.
      Now with the merger of Airtran with American Airlines another low cost airline will be consumed by a "legacy" carrier and you know that will not mean that they will try to be a low cost airline after the merger.  I know that other low cost carriers may look at BWI but will they fly to many cities?  Will we be forced to endure a trip to Dulles to get a good deal on a flight?  The idea of having to get on the Capitol Beltway to get to Dulles always makes me think twice about booking a flight from Dulles unless I can arrange the flight to avoid rush hours on the Beltway. Somehow that 20 minute trip to BWI seems to almost always win out over the dreaded trip to Dulles.
     Airline mergers seem to never have a benefit for the consumer.  Fewer choices mean high prices.  Low cost air flight seems to be something in the past.

P.S.
   The Seattle Times had an interesting article recently about how to time your reservation to get the lowest cost.  Seems like making your reservation about seven weeks before flying is the best.  Booking farther in advance isn't going to get the best deal.  Tuesdays are usually the best day to book a reservation. Saturdays are usually the best days to fly.