The thought that an airlines can diversify their way out of the risk of a rare grounding is foolish. Even if WN bought a second type and was split 50/50, losing half the fleet is catastrophic.
Rare? In the last six years there have been two major groundings of Boeing aircraft. Not only that, but the engine issues on the 787 and A320NEO have resulted in partial groundings.
WN is an enormous airline with 750 aircraft. This is such a huge fleet that they are way beyond any economy of scale. They could easily introduce a second or even a third type and still have enormous enough fleets to benefit from economies of scale.
WN put all their eggs in one basket and now they are suffering for it. And if these pickle fork issues on the NG turn into something, WN could wind up having to ground an enormous portion of their fleet. They have every reason to start to consider that maybe having an airline that big with that much risk exposure based on a single type is not a great idea.
And Airbus has no incentive to cut anyone aggressive deals on A320neos at the moment with their backlog the way it is.
For Airbus to break into one of the largest all-Boeing operators in the world (gosh, if not *the* largest) they have no incentive? They have a *huge* incentive.