I think the main point here is that SW isn't going to see any increases in the total number of aircraft for quite awhile, they are in replacement/realignment mode right now. It's going to be a very long journey up that seniority list for the folks near the bottom. A long time on reserve, a long time in undesirable bases, a long time working weekends and holidays and a very, very long time in the right seat of a 737. It's like a game of leapfrog, SW had their time and got way ahead now they will wait while some of the other carriers catch up and go past them.
Before long the Big-3 are going to be in high gear when it comes to hiring and promotion and SW will be hiring/upgrading few pilots. Part of the SW culture over the years came from fast growth and promotion, the airline went full-throttle for years and pilots hired at the right time had a great ride. Will the culture change (at least for the pilots) now that the music has stopped? I think there will be a lot of talk about cost at SW but very little talk about growth. SW should still be a good company and a good job but the rapid career progression is probably over for 15 years or so. All the CA's they will need for the next 20 years have already been hired.