But in this extreme case of the fuselage being inside the wing and making it much thicker than typical and necessary, this isn't necessarily true, at least it's not obvious.
If this design actually provides the claimed results, connecting 2 such wings (one behind the other) with a long fuselage (i.e. >---> which would incur almost no additional drag and twice the lift) would be even better, no?
Think of it this way: A cylindrical fuselage provides no lift (except for the lift from its angle of attack flying obliquely through the air), only drag. If you can design the aircraft in such a way that all exterior surfaces contribute to lift, that would be ideal.
The "---" portion of your idea provides no lift, only drag.
The ideal flying wing is more efficient. The tradeoff to make a flying wing suitable for commercial aviation has historically made those efficiencies moot.
