I don't see the big 4 getting into price wars with each other, but I do see them reclaiming lost markets.

The airlines are making money hand over fist right now. In business terms, that means a war chest. The time to kill the startups will be during the next economical down turn. You hedge your loss. Buy them, or price war them into bankruptcy. The later being the more economical option if the targeted company has low cash assets, and no callateral equity.

Who is that? Sun Country is not cash ripe, and they lease everything.
Frontier I believe is owned by a holdings company (think shell game to strip the cash). Spirit? Not sure about their structure.

So, as a bean counter what do you want? You want their market share. You don't want their debt or leased planes. You "drive them out". I think Allegiant, Frontier, Spirit, etc won't be bought, they will be the next targets of the big 4. Of the 4 who has the war chest? SWA and DAL.

Just one guy's take