Long flights
I will say this, having had to do several long flights this year:
1. It's difficult to look at the benefits/disadvantages of flying direct vs flying a kangaroo route (i.e. one or more stopovers) without actually having tried it. Those who have flown Perth-London/Frankfurt or Singapore-New York are probably the ones most qualified to answer since those are the only non-stop flights that are roughly of the length that Qantas are planning to fly. Maybe those non-stops from Doha/Dubai to Auckland/Christchurch are alternatives because they are also very very long flights (the longest in the world other than the Singapore Airlines one). Note that SIA's nonstop to Newark/JFK is all-premium, so there is no Economy class on that flight (unlike Qantas' non-stop Perth-to-Europe and soon-to-be Project Sunrise offerings). SIA have previous experience, having used an A340 (also in all-premium layout) to Newark before killing it until the A350-900ULR came on-stream.
2. I agree with others that either flying Premium Economy or Business is well worth the money, if only for the slightly better layouts. Of course Qantas will absolutely milk their offering for what it's worth (which it will be - ask SIA about their non-stop service to New York), because no-one else does it (yet). Having had to fly to Japan and Southern Africa (Africa was shorter), I very much appreciate a lie-flat business seat (because you can actually lie and sleep, provided the crew don't turn *up* the heat instead of down). Emirates has added some new tweaks to their latest Economy seats that should improve how well you sleep in Economy (built-in wings that give your head support), but nothing beats lying flat with no constant stress on your spinal column and your ass for 20-odd hours.
3. There's a reason why Doha, Dubai, Singapore and Istanbul have the delightful airport experiences - They are there to decompress you from your previous flight, give you relief and some stimulus because you get on the next one. Both Istanbul and Singapore have made a layover an opportunity to look at their host cities (even just for 12 hours) - I can't speak for Doha or Dubai. Sometimes just having that break makes a big difference, consider that a bonus.
My personal preference is that if I *am* going to be stuck in a tube for 22 hours that I will a) fly business (or premium economy at a stretch), and b) ensure I move about regularly (a lap or two around the plane along the aisles makes a difference, provided I don't get in the way of the crew preparing for service). And having a decent business class seat is important too (the 'old' business class on Turkish, whilst not a "suite", is pretty damn good because you don't feel like you're in a coffin, the newer door-less staggered business class on Swiss, for the aforementioned coffin reason, is not). Doored suites (the newest type of business class on many airlines) are good in the sense that you will have guaranteed aisle access and don't need to bother your neighbour.
If it's not possible to get a decent business class seat for non-stop, I will do a single layover at a decent airport with a break long enough to take a walk but not so long that I am begging to get back on a plane (2 hours or so in Istanbul was a great break). If the airport offers bedrooms/pods/airport hotel for a longer break, go for that, if only to lie flat for a little bit. So unless Project Sunrise flights are priced decently, I'll be hopping through Singapore or Istanbul, if only because the airports actually are very good.