OK, now I know I have asked this before, but here's an interesting question.
IF NW took West, and UA took East, in theory, at least, would it not make sense for East and West to swap Airbus 319 and 320 aircraft before such a transaction closed? NW and East use CFM-56 engines and UA and West use the IAE 2500's if I remember correctly. The 321's and 330's could go to NW as well, to maintain fleet/engine commonality. NW already has 330's. Of course eventually this could leave the flying pigs without homes (321's), unless they could go to F9 or something like that.
It seems to me operating the same type of aircraft with two engine types makes no sense whatsoever. While the transaction would be complicated, the Airbus fleets would match perfectly, leaving only the 757's if I recall correctly with diverse engine types.
And while I am dreaming, NW already has a large fleet of 757's as does UA, so the entire fleet of RR powered 75's could be disposed of.
Of course this could never happen, because it makes TOO MUCH SENSE..... but what if..........????