hawkeye,
Qantas and Emirates for some time now are operating A380s on sectors which are longer than LAX-HKG, and they doing do so very comfortably with the "A" model.
LAX-MEL has a sector length about 10% longer than LAX-HKG with similar sorts of total average winds that Cathay could expect during winter. Previously Qantas operated this sector with a 744ER (only airline with the 400ER passenger aircraft) with a much reduced seating configuration just to make it.
EK are now operating the A380 on routes they previously operated the 777-300ER, e.g. their daily EK412 (DXB-SYD-AKL-SYD-DXB). Their president has said the A380 is burning 20% less fuel per seat than their 777-300ERs. That is quite a feat when you compare their seating on the 777-300ERs is about 20 seats (2 rows of economy) shy of what Cathay put on the 744.
Cathay would not gain much capacity at all if they put a Premium Economy class into the 747-8I (4 class aircraft), however using a more generous seat pitch and width on the A380 would result in about 70-80 additional seats with the quietest cabin, and excellent IFE. Singapore airlines on their regional services have been having consistently high loads factors on the A380, while load factors have dropped on their competitors. The A380 flights I have been on have been 100% full.
I do not think many of the common detractors for the A380 are holding much water these days given the aircraft now has 3 years of operational experience with 4 airlines. If Cathay was to get the 747-8I it would still be the "A" model, if they went for the A380 it would be the more mature "C" model that start being delivered to airlines onwards from 2012.
The A380 would also have crewing efficiencies, with A350 crews able to fly the A380, the same efficiencies would not be available on the 747-8F/747-8I.
Media reports of the only two airlines that purchased the 747-8I indicated that it was allegedly as part of a compensation settlement with Boeing. Lufthansa it was due to the money they lost when Boeing decided to close down their inflight broadband service (Connexion by Boeing) a short time after they have spent US$500,000 per aircraft to install the hardware and Korean due to their ongoing 787 and 747-8F delays.
I do not think Cathay would operate a new large aircraft on any route exclusively, I think they would do so with a combination of frames, e.g. a mix of 777-300ER and 747-8I or 777-300ER and A380 frequencies to LHR would be more likely than all frequencies with one type, that would prove the best mix for passenger and cargo capacity increase while still giving operational flexibility.
I do not think Mr Tyler has expressed any view that is different to what the previous CEO had said a few years earlier, I think they are still receptive to considering both airframes, but that could translate into no order for either as well.
All of the above is my personal view, Mr Tyler speaks for the company.