The article also fails to mention the young fleet age of UX, as well as the shift of domestic capacity to UX. Perhaps the reason UA isn't in a hurry to make a narrowbody order is because outsourcing the flying to the lowest bidder is more profitable than doing the flying on mainline equipment.
I am sure in the next round of pilot negotiations, raising the maximum seat count for UX operated flights will be a key negotiation point... not sure ALPA will agree with it.. but you can argue that UA's mainline network (especially international) will become a lot stronger if short haul domestic flying can be more profitable.