New York Magazine has just published a long article on airline economics, centered on its most profitable element, Delta Air Lines: “We Love Delta. We Hate Delta — It’s been a hellish time to travel, but one airline is winning by catering to the elite. Good luck to everyone in coach.” by Ben Ryder Howe.
Here’s a quote from near the end:
“The industry is moving toward elite clientele,” says Stephen Milstrey, a veteran airline network planning and scheduling executive who has routed planes for Virgin America and Frontier. “Eventually the big airlines will minimize the main cabin and let Frontier and Allegiant handle those people.”
Or, as is happening in Japan, according to the article, they can just stay home. With the demise of Spirit, my guess is that this opens up competitive space for someone who can figure out how to exploit it. Not necessarily another airline.
If you have Apple News, you can find the article at: https://apple.news/ARKzMW_FGRIigjAkpBzD7bg
You can read “Logical end to the K-shaped economy” here: https://slightlyeastofnew.com/2026/01/21/logical-end-of-the-k-shaped-economy/
Slightly East of New 
One of the major factors in the death of Spirit is the fact that the “majors” cracked the code on basic economy seating. They now provide what Spirit provided: minimum legroom, no refund, no frills, cheap fare in the back of the bus, but unlike Spirit, they have the network of a big airline, the reliability of a big airline, the mileage programs, and the status of a big airline. Mid-class folk complain about how heinous it is that basic economy takes away so much that we take for granted. It’s not for us. Basic economy is for the folks who used to fly Spirit.
Spirit died because Delta, United, and American out-Spirited Spirit. They did Cheng and Chi where Spirit only did Chi and in the past they had only done Cheng. Something new did emerge–and that new is what killed Spirit.