I don’t believe they were the only airline that ever used open seating. But it did create an incentive to show up early at the gate when they had plastic, reusable boarding passes. Then it was a mad rush at online checkin time when boarding order was assigned.
After listening carefully to Customers and conducting extensive research, Southwest decided it will assign seats and offer premium seating options on all flights. The airline has been known for its unique open seating model for more than 50 years, but preferences have evolved with more Customers taking longer flights where a seat assignment is preferred. Additionally, Southwest conducted robust operational testing that included live and over 8 million simulation-based boarding trials. The airline is confident that these Customer enhancements will meet expectations and not compromise the airline's operational efficiency.