The rumour mill is rarely wrong in my experience, and there’s been plenty of circumstantial evidence that Airbus will be Delta’s choice.
For one Delta was not amused by Boeing’s attack on Bombardier which directly affected its 75 aircraft order for CS100’s.
Additionally Airbus and Delta have a surprisingly strong relationship – Delta are the only current operator of the A350 for example, everyone else has deferred their orders. It’s also been an enthusiastic A320 series operator, along with A330’s.
In many ways this order will be Boeing’s to loose as the 738Max was high on Delta’s shopping list. But the A320neo looks like it may have come out as favourite.
I suspect Airbus may have been able to sweeten the future of the CS100 order as well, making their deal even more attractive.