As for the wing, it bears investigating. MTOW is not going up, so there was no need to significantly increase the wing area and weight.
The requirement to increase area was born from the low cruise levels requireed at high weights hampering performance and better matching the engine limited and wing limited climb/altitude performance. MTOW increasing is all but moot for the wing weight as MTOW very little bearing on this, the weight it is driven by is MZFW.
In addition, since the wing cross section is not rectangular, where Boeing chose to add area is significant.
They haven't added area to a part of the wing, they have designed a new wing and they have to account for and design the wing according to the aerodynamics AND structural capabilities of the WHOLE wing.
Adding area to the far edge adds less weight than adding to the wing root.
No, the inboard part of the wing has to carry the loads of the outboard part of the wing whether you add the area there or not. Adding area to the inboard part of the wing on a tapered wing will have a two fold effect of not increasing span (and therefor moment arm of a lifting surface) as much as the outboard area increase but will also allow the section being added to be of greater thickness (assuming a similar t/c to maintain similar transonic drag levels) and so have a lower compression buckling from the wing bending moment.
So the increase need not be as straightforward as a volume rule.
It isnt ^3 because it is a volume rule, it is because the derivation of how moments are carried in the members of a cantilever structure give rise to the loads carried and the material required to carry those loads.
In any case, the known 779 case can be worked backwards to the known 77W to fill in some gaps. But that takes time.
Agreed, thats where the 168-170t figure came from.