I keep hearing the A380 supporters arguing that it improves efficiency at slot-restricted airports. But this may not be so. Due to wake turbulence, aircraft following a Super must generally maintain larger distance separations than when following Heavies. Further, gate and taxiway limitations may also increase Super handling costs and thus reduce airport efficiencies.
Finally, to quote Juan Trippe of PanAm -- what he means by aircraft "payload" is not the total weight carried, but the load that pays. It doesn't really matter what is more comfortable for the PAX, if the extra amount they are willing to pay for extra comfort does not exceed the extra cost of providing this comfort, the airline ain't gonna provide it. Further, this calculation is based on how much the average customer values this comfort and is willing to pay for it. If an individual customer (or small groups of customers) has a higher valuation, the airline is happy to accommodate them in Business or First Class (at their rates). They will not accommodate them by improving the overall comfort of Coach.