Perth is so small it has a daily EK380 plus every other airline serving it with 777s 340s and and 330s.
If it's that good then why did QF stop international flights from there ?
Perth may be bigger than Brisbane in a few years but the catchment area is negligible outside the city. In QLD, unlike other states, most of the population live outside the capital. BNE will soon be a LAX style spread from the Sunshine to Gold coasts.
The configuration of a 787 in 9 across is similar to an A320/B737 typically used for much shorter journeys. The flight would be hell, I've done 14 hour legs in the A380 and the B777 in 9 across and was more than ready to get off. Imagine 18 hours in a domestic B737 configuration. I avoid the B787 as far as possible, A350 is much nicer.
With the ultra long range A350s being developed for Singapore Airlines to fly to the US, SYD - LHR might be possible a few years down the track with advances to stretch the range bit further.
An overnight break in an airside transit hotel in the desert makes a journey far less tiring. Two legs with a good night sleep in between reduces jet lag and you can adjust your arrival to a convenient time by choosing a suitable connecting flight.