I wouldn’t be shocked to see F9 for sale, but I highly doubt that the largest airline on earth (AA) would be allowed by regulators to buy it.
I could see the strategy for UAL to buy. AA and Delta have 19.5% and 16.3% domestic market share, respectively, along with WN’s 17%. UAL sits near 12-13%. I could see acquiring F9 and their 3.5% as a sound strategy to achieve parity with the others. A young fleet of NEOs would also fit right into their plans of a fleet refresh, not to mention an influx of pilots, and giving another leg up in their battle with WN over Denver.
I don’t think Delta has any need to purchase. WN, maybe??
Fun to speculate, but in reality I highly doubt any of these would happen. Maybe F9 and G4 find a way to play together? Who knows, but it does seem like there will be some big moves in the industry at some point soon.