They HAVE Airbus order:

http://www.airbus.com/en/aircraftfamilies/a300a310/a310/

Note that the A310 order count is still 260. Airbus has not cancelled the 5 A310 yet to be delivered.

I wouldn’t read too much into the Stanford study. It is a trend recognition, but it fails to take into account the practicalities of building larger and larger aircraft. There is a finite amount of stress that current materials can take, which increases with size, and what the study fails to note is how the weight of the aircraft itself starts to rise rapidly as we apporach the finite limit.

I do note the lack of structural/OEW estimates in the Stanford study. Maybe they did it, and then did not bother to give numbers. What they do seem to say is that wing weight is small enough that even if it does undergo square-cube increase, it still remains a minor factor.

As I said earlier, we are about there in terms of limit, unless we get some major advances in material technology. Otherwise, as Schorsch noted, the aircraft will be carrying more and more of its own weight, with a lower and lower useful payload.

For example, compare B-36 with B-29. The 70 m wingspan of B-36 is bigger than any jets till An-124. Yet B-36 has a huge useful load and long range. At which wingspan would the structural weight start to seriously limit useful load and range?

What about An-225 and Hughes Hercules wing structural weight?

With limitations. The structural weight increases fast than weing area (so called square-cube law, structural weight increases as cubic function of size while wing area only as quadratic function).
The solution is either increase of the wing loading or reduction of the volume-specific structural weight, or of the loads acting on the aircraft.

The A380 is in the end of the useful region, anything bigger than the A380 will become less efficient and primarily lift its own weight.

As for square-cube, see

http://aero.stanford.edu/bwbfiles/largeACopt.html

The limit does not seem to be nigh.

Problem is that this fuselage needs to be lifted, and even on the A380 it gets increasingly problematic to accomodate for the wing root. The loads acting on the intersections of fuselage and wing are tremenduous and a reason why the A380 is quite a heavy beast (more OEW per pax than a B747).

One restriction for A380 is the 18,3 m limit between exits. It matters because A380 is a doubledecker.

For a single deck airplane like Concorde, overwing exits is no problem, which is why Concorde has 29 m root chord.

However, A380 is a doubledecker. There is a pair of overwing exits – on main deck. If you look at the upper deck, it has exits just ahead of wing leading edge and just behind the trailing edge – the slides have to go clear of the wing. The maximum 18,3 m distance between exits means that the wing could not be made any wider than it is.

(Could the matter be fixed by a middle staircase, or could it not be done?)

They say it will be the
largest (a 14 inch wider cabin than the G550..and three inches taller),

Yes, but G550 is notoriously narrow compared to Bombardiers.