I certainly don't think that CX is going to change its mind on operating a mixed fleet. The 747-400s, 777-200s, 777-300s, A340-300s and A330-300s are working quite well together. The addition of the 777-200ER to the fleet would only strengthen it. I must say though that the recent decision to put off a new order has pleased me. That means that my name sake CX 747-400s get to be the "Top Dog" at Chek Lap Kok for that much longer. What I do find interesting is that this important order has been put off once again. The last two times this happened, the entire purchase was rethought. While it would take some fanagling, getting the 777-200ER into the CX fleet is in my opiinon a very good move. Just as the A330-200 is superior to the 767-400ER, the 777-200ER is superior to the A340-300. It moves more people, more cargo, a further distance at a faster speed than the quad. Along with doing it for less cost due to the big twin engines (One would assume RR Trent 895s for CX). I truly can't say whether or not I think this will effect the future order (A380, A340-600, A330-300), but I do think that the -200ER will find a home at HKG and it will be welcomed with open arms.
Just for kicks, what if Boeing were to offer CX a deal like SIA! Take in the A340-300s, sell them 777-200ERs along with 777-300ERs. This would be a fantastic move by Boeing and one that could also land them a 747X order.
Another interesting issue over at SIA is the A340-500.
Supposing that both it and the 777-200LR live up to their "paper performance" the -200LR carries more people, more cargo, a further distance and faster. So, if the A340-500 is found to operate the SIN-LAX route profitably, then SIA will most likely test the -200LR. Could we see a repeat of the A340-300 dump off in favor of the -200LRs older sibling the -200ER? Only time will tell!
"History does not long entrust the care of freedom to the weak or timid." D. Eisenhower