"There have been arguments about whether people want to fly twins on 18+ hour flights"
Which to me is an utterly senseless arguement considering that a 14,15, 16hr flight (be it over land or water.... or most likely both on a flight that long) is to a pax no different than an 18hr. Witness EWR-HKG, CAN-LAX, HKG-LAS, etc.
I personally would much rather be on a twin and no more than 3.5hr away from land than much have 2 extra engines.....
Faire du ciel le plus bel endroit de la terre c'est impossible sans Concorde!