The thing is, the A380 shows the problems with a true double decker. This is about as short as they could practically go with 2 levels. Maybe the 6 on top, 9 on bottom would work, but it would be structurally inefficient.
What support do you have for these assertions?
The record supports that the A380's form was dictated by the 650+ seat capacity target. Airbus specifically explored double-deckers as small as 8-6 but found that, at 650 seats, the fuselage would be too long and heavy (and maybe not fit the 80m box).
In other words, Airbus wasn't even trying to go "as short as possible," they were trying to go as big as possible.
That's the fatal flaw of this whole program: the capacity tail wagged the efficiency dog.
It simply wasn't and isn't possible to deliver a -900-sized plane with an 80m wing; Airbus should have responded to this constraint accordingly.
Virtually any double decker of 8-6 or bigger cross section could have been built with about the same efficiency - measured as wetted area per pax - as the A388. This is even easier if you forget about Airbus' desire to have a potential "triple-decker" - the current cargo hold can be fitted to accommodate pax amenities - and go with a shallower belly.
The so-called winglets, which on the A380 would each measure as much as 5 meters (16-feet), could reduce fuel burn by up to 4 percent by dissipating the vortexes of rapidly spinning air created by the plane’s wings.
It would be interesting to see drawings. Just from a quick eyeballing, it seems very difficult to achieve the optimal blended winglet (parabolic slope from the wing axis) without revising the outboard ailerons - which would be expensive.
OTOH I would have guessed more than 4% benefit for the A380 from optimal winglets, so maybe they've found a suboptimal winglet absent parabolic blending that still brings significant benefit. Given the A380 drag breakdown's heavy tilt towards induced drag, even a suboptimal winglet should deliver significant savings.
Another good quote from the Bloomberg article:
“We will not launch an A380neo, there’s no business case now to do that, this is absolutely clear,” Bregier said.
If only Bregier had deigned to weigh in our dozens of A380NEO threads over the last few years. Somehow I suspect even he'd be dismissed a "basher" though.
Let's keep this quote handy for the zombie comments on solving the A380's problems with the long-dead NEO.