I am aware southbound, LHR-PER is shorter, but the list of suitable alternates in the Indian Ocean is a lot shorter too, if you are chasing the Westerly they will be south of Sri Lanka, 180 mins from Jakarta then its Port Headland and PER. Then even if you have 10T-12T on arrival PER, You won't make ADL, and really, who wants to go to Learmonth or Kalgoorlie?
Ushuaia,
PER-LHR, sure, duty time will be restrictive, but i'd rather be in a hotel in Frankfurt/Rome/ than the airport terminal at Learmonth/Kalgoorlie/Port Headland and running out of duty.
Add in Karratha to that list also...
It’s unlikely hotels would be needed, other than in exceptional circumstances.
Barring other delays out of the departure end, there should be plenty of duty remaining for a gas and go stop if needed, all those ports should be capable of it at that time of day. There should also be standby crew in Perth to pax one of the many qanta... erm network a320 services
to pick it up should that be needed. Or have one of those idle a320s
come and get the passengers. (Not ideal but not a game changer-stopper).
Adelaide fuel is something like 14t overhead Perth, btw.