So a 17.5 hour direct flight + getting to and leaving airports. Hmm! Last time we did Sydney from London we stopped off in Bangkok going and Hong Kong on the way back. 11.5 + 5 hours or so was a long time, but 17.5 hours in one? I really don't relish the prospect in an upright economy seat. I can't snooze or sleep for more than a couple of hours at a time even with low cabin lights, there is just too much going on. A flat bed/seat would cost too much, and even then you wouldn't sleep for all that time. On an 11 hour cross-channel car ferry we have a proper en-suite cabin with berths and that's fine. Something similar on the aircraft, a mini-cabin, might work but cost more, of course, but I just cannot get excited about long distance flights at all, unless I have to.