I wouldn't be so dismissive. I'm sure they ran some simulations on this. With 3 sets of wings, the plane would have much more flexibility with the center of gr

I wouldn't be so dismissive. I'm sure they ran some simulations on this. With 3 sets of wings, the plane would have much more flexibility with the center of gravity. With two wings this needs to be where the wings are. This is why fuel is put in the wings in such configurations. It's a good design if you only have two wings. With 6 of them and the engines mounted on the back, you can play around a bit with different weight distribution. I'm guessing that using fuel bladders on top of the roof would allow for flexible placement anywhere between the first and last set of wings. Also, you can pump fuel around as well to change the weight distribution (and possibly even trim the airplane's pitch). Drag of modern planes is quite optimized for their current designs. However putting the fuel in the wings and mounting the engines on them probably adds a fair bit of drag regardless. Also such wings have to be bigger and stronger. I've had a window seat next to the wings of an A380; they are massive. So, I can see how changing that configuration that could eliminate some drag. And using modern composite materials without seams is also going to help with both weight and drag. Less weight means more fuel savings. If it adds up to 70-80% will be interesting. IMHO the real issue is going to be getting rid of kerosene as a fuel. Synthesized fuels like hydrogen or methane could potentially be a lot more sustainable.