I don't think AA are currently in any financial position to negotiate the world's biggest aircraft order. The idea of them announcing a 450 aircraft order is suicide with the state of the US aviation market.
Maybe if one of the big airlines goes bust (Delta or United) they will be in a more secure position.
How many 738s do they have left on order, if any? (Not too sure on numbers)
Maybe these could do a job of replacing a couple, other than that, I wouldn't be surprised if AA does a Northwest and works the super 80s to death in the same way Northwest are doing with the DC9's, with some of them being 30-40 years old.
With Northwest I reckon if anything they would replace their DC9's with Airbus as they seem to be quite a loyal customer with their amount of A319s/A320's and A330's and Airbus are more likely to do a deal with them to snatch orders from Boeing.