Out of interest, once you've factored in the extra costs accrued through additional hotel stays, days needed for the trip given longer stopovers and so on, at what point does it actually become more cost effective to fly in a higher cabin? As you say I'm sure this would work well for people with no time constraints on a trip that is purely for leisure purposes but it's not for everyone.
It's absolutely not for everyone. I don't really include the costs of the multi-day stopover in consideration, as I really love Asia and to me that's part of my holiday, and if I wasn't there I'd just be paying hotel and food bills in another (more expensive) country. Others may of course disagree with this approach. Anyway, some numbers from my last trip:
MH Y flights for me and my wife LHR->KUL->SYD return were ~£750 each, plus ~£50 each for extra legroom, plus ~£60 for Heathrow and KUL hotel overnights.
So that works out to about £830 each. For a similar flight from LHR in J I think you'd be looking at around £2k each? My wife has no interest in ex-EU and is Scottish, so would never approve of blowing an extra £2k for better seats on a flight!