To be perfectly honest, this number sounds speculative at best (utter nonsense at worst). The fuselage is generally about 20-40% of the entire dry, empty weigh

To be perfectly honest, this number sounds speculative at best (utter nonsense at worst). The fuselage is generally about 20-40% of the entire dry, empty weight of an aircraft (speaking strictly about large transport aircraft). So clearly seeing that kind of reduction in weight isn't really possible strictly from structurally modifying the fuselage (and even major modifications of the entire airframe). If we look at comparing planes with windows (like those operated by passenger airlines) to those without (like those operated by cargo airlines), loose estimates are less than 1% to around 1% weight savings from removing windows alone. Even if you assume massively increased returns on weight savings because of massive changes in airframe design it's probably no where near 50%... Keep in mind, even incredibly small weight reductions mean huge savings over the lifetime of an aircraft (especially if they are also carried out over an entire fleet).