I agree with AA777
I will be curious if the A380 will be as fast as the 747-400 series (someone may know the answer to that).
The 747-400, and more specifically the ER
version, could feasibly be manufactured for another 10 years. That would put a potential retirement date of 2033! That would have to be a record for a series of an aircraft. Granted the 747-100 and 747-400ER are quite different!
I wonder how far the 777 program will go. Is a -400 or -500 out of the question? The 7E7 still has some discussion on placement.
If there would be a replacement, a 777 series - 777-XER would be the replacement - more pax, another 500 miles range from the 747-400 ER
A 747-500 or 747-500ER sounds scary! Imagine a wing with two GE
90s or bigger on it!!! That would need to be a very strong wing!