The ULCC model is over, and the Big Three have seen it, with even Southwest showing signs of the shift. Gone are the days of Song, Metro, and Ted. The Big Three now simply need to saturate markets with "Basic Economy" seats to undercut Spirit and Frontier, whose strategy was to target the major hubs and take the cheaper flyers. Airlines like Alaska, Hawaiian, and JetBlue also see this, which explains why Alaska and Hawaiian are expanding internationally, and JetBlue is struggling to remain competitive. I don't believe Frontier will be much better off even without Spirit. We are finally seeing the self-correction of deregulation, though it's taken 40 years.