Hi Lucas,
Difficult question.
747s, 787s, 777s and direct replacements are fenced for 5 years from SOC (Jan 2010). Doesn't matter how many they get, and current fleetcounts don't matter.
Ex 1: Delta buys 10 747-400s over and above existing orders. fNWA guys fly them exclusively until 2015.
Ex 2: Delta takes delivery of 10 777s they had on order, without replacing any other aircraft. fDAL guys fly them exclusively until 2015.
Ex 3: Delta buys 777-F all cargo variants. fNWA guys would PROBABLY fly them exclusively because they are a direct replacement for the parked 747-200Fs
Ex 4: Delta takes 747-400s in trade for 777 orders OR 777s in trade for 787 orders. In that case, warm up your checkbooks, because thats when arbitration starts.
Richman