Either jetBlue and AS merger and still be the #5 biggest carrier competing with the big 4. OR. One of the big 4 buys jetBlue. If that happens, one of the remaining 3 big carriers would be forced to buy AS to compete better and get bigger themselves. Of course this assumes that the ULCCs only merge with each other. If jetBlue merges with Spirit/Frontier/Allegiant/Sun Country then the big 4 may not care as much.