To save space, why not make shorter, double-decker variants of?
Aerodynamics would become like a brick. The plane would use the same amount of fuel to fly half as far, or twice as much fuel. A larger frontal cross section causes more drag, which needs to be overcome with thrust. Your plane would burn fuel like it was the 1960s all over again. Current airports dont have a problem with aircraft length anyway. The new Boeing 7778 and 9X have folding wingtips because their WINGS are too wide. Changing the length of the aircraft wont help there.