This is a VERY intriguing discussion.
First, doesn't the combined US still have 30 Airbus A320 fam deliveries deferred until 2009 or so? (19 from US Airways and 11 from America West, IIRC) Neither bankruptcy nor merger caused those orders to go away, just to be deferred. Are those 30 included in this "new" replacement order?
Realistically, the "new" A350 XWB seems to be a bit more a/c than the 767, so the leaves the 787. The -8 version will carry 210 - 250 passengers on routes of 8,000 to 8,500 nautical miles, which is a tad bit more a/c, too, then the 767, but that range seems to open up PHX to Europe markets, PHX to Asia, and even PHL to Asia, I believe... That range is HUGE and opens up A LOT of opportunities not previously considered. In fact, why would US even need to keep around the A330s, if the 787 can do the same job, or better? It's a beautiful aircraft that I don't think Airbus will ever be able to compete with. Many, many executives at US have been heard to say how much they like the 787. What is there not to like about it? But that doesn't mean US is going to order it, necessarily. It's all about the deal, the money, the financing. And, don't forget, too, Northwest already has 787s on order (for all you merger/rumor mongers!)