When you stop thinking of AS as a legacy airline and start thinking of them as just Southwest with a First Class, two things will happen:
1) All of their miserly decisions will start making much more sense.
2) You'll be able to predict with stunning accuracy what they will do in the future.
Simply ask yourself: when will WN add a premium economy section? If the answer is never, then you'll have a pretty good idea of when AS will do so.