Well I have to agree in some aspects that UA will go with the A320 family in the future, and I must agree with others.
Kona, I believe you are right about UA being done with the 737s, but only the CURRENT 737s. While Ua is obviously saying that the replacements for the 737-2/3/500s will be of the Airbus family, that doesn't mean that UA won't buy the 737 NG somewhere along the line.
Being a UA fan, you know that UA is starting to make an effort to improve its reliability and economics, correct? They are alos upgrading their service to a point, and making the passenger experience better. Good customer winning strategy they are getting into, beats the other method of simply cheaper fares on select routes but a lack in service.
Well any smart business knows that putting on this image is just fine, but you must do it ECONOMICALLY. That's where the A320 family comes in. See, pax lately have really been wanting more leg room and wider seats. The A320 family provides this without forcing the airline to remove a row of seats, thus more economical. Use AA as a model. Their nearly all-Boeing and Douglas fleet needs to have a few rows of seats removed to create more leg room.
What this does is lessen the economics of the remaining passenger load, driving fares up, and profits down. Of course, the higher fares aren't very attractive to a would-be customer, and business is taken elsewhere.
UA has the upper hand if they go with the A320 family.
However, that doesn't mean that they won'tr buy Boeing's in the future. As you know Boeing is fighting Airbus, and striving to upgrade their product to match what Airbus already sets as standard.
Therefore, Boeing might strike a deal with UA, to provide a new 737NG with equal or better aspects than an A320, and UA might go for it.
But if Boeing does nothing, you'll definitely see alot of Airbusses in UA's fleet within the next decade, for sure.
One more note, though. I don't think UA will do both. It will either be Airbus, or Boeing. As you also know, it is not economical to keep spares piled around for both types, it is cheaper and much more feasable to keep parts for one type, and have the entire fleet be that one type. It's just simple and much more practical.
So, what I think is that you are right, UA will buy Airbus products and stick with them.
Only time will tell.