LOT 737-300

There is also the question of capacity too. You can't get the passenger capacity of the 747 in either one of those two. But since UAL seems to be backing off the 747 for now, the more logical move would be the a larger variant of the 787 or A350. Of course, I'd expect the 787 and A350 to be more fuel efficient than a type designed when I was born simply due to logical progression of technology. I'd be worried if a 787 would find itself doing worse than a 767-300 in terms of fuel economy.

BUT there is one place where Twins may be limited in place of quads, and that is operation over water, where operational protocol such as ETOPS may limit how far from land an aircraft with twin engines may operate (LOT's former director, Wilanowski mentioned on how LOT's IL-62s could make it to Chicago or JFK in a shorter amount of time than the 767s because of ETOPs limitations).

Of course, as time goes on, it using the idea of using 4 engines to get around that becomes more obsolete as ETOPS ratings get pushed further and further away from Land. ETOPS 180 already covers around 95% of the planets surface if I'm not mistaken, and some aircraft (i.e. 777) are approved for ETOPS 330. So in that aspect, a Quad is obsolete. I'm not sure of the A350's and 787's ETOPS rating, but I'm sure they have at least ETOPS 180. In fact, I wonder if the 777 getting the ETOPS 330 and the 330 getting the ETOPS 240 rating helped start the ball for many A340 operators to start replacing said A340s in recent years.

And of course, the last point is this, it isn't just capacity or fuel consumption either. There is also the question of maintenance. Logic should dictate that maintaining two engines instead of four will cost less. This lower cost, means is also a huge incentive for airlines who want to cut as many costs as reasonable.

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My Airport: Nowa Warszawa Int'l (NWL):
Attempt at first model airport (2005ish?)http://www.freewebs.com/nwlairport
Hey, model plane manufactures, how about some Braniff PZL 230Fs.