SFO is a much different scenario though. SFO is a hub for UA, but not on the scale that ATL is for DL, where they control nearly 80% of the traffic; thus AS can peacefully coexist alongside UA. Additionally SFO benefits from a strong local traffic component vs connections.....somewhere along the lines of 70% vs 30%, whereas ATL is around 40% and 60% respectively.

AS will eventually need to expand east, continue to rely on AA to provide the midwest/east feed, or risk becoming the west coast merger partner of B6. If I'm playing armchair CEO, merge AS and B6 renaming it as JetAmerica, and open a central hub in STL.