I'd put money on the likelihood that the initial flights are capped in both directions for the first few weeks (if not, even permanently). So any talk of the loads potentially being low should probably consider this. Any diversion or flight that doesn't make it in the early time period of the route operating will be a
PR disaster.
The higher cost of the tickets probably not only reflects an attempt at charging a premium for a non stop service (well, non stop out of Perth anyway), but also a way to buffer the loss from a whole bunch of economy class being blocked off.
Its been no secret that ultimately QF see direct, point to point, ultra long haul travel as a major area they want the international business to grow. There has been a desire for an aircraft that can do SYD-JFK, and MEL/SYD direct to LHR, and obviously those would be a premium service at a premium price. Per-Lhr is a route that starts to give people the idea that these routes are possible and are worth the extra coin, so that when the Aircraft that can do those new routes profitably come into existence, they can point to the ULR routes they have been doing for years and say they are the old hands at it all.
I can see the company accepting that the route itself may not be very profitable, if at all, at the expense of reliability, only to have created a market whereby the company basically positions itself as the market expert/leader.
Playing the long game, if you will. Ofcourse, I could be giving management far too much credit.