What is the structural impact on the wing if no fuel is stored in the wings and just in the fuselage?
This has been well-studied, here are the basics.
For the case of fuselage tankage for fuel: The structural loads caused by the weight of the fuel in a fuselage tank must be transmitted between the wings and the fuselage. This means beefing up the wing-to-fuselage attachment points, which is not required if the wings carry the tankage instead. Putting the tankage in the fuselage also means less room for passengers and cargo.
The best place for this fuselage tank would be right at the center of gravity so the CG shift with fuel consumption is minimized- which unfortunately puts the tank right where the passengers sit. And because this places fuel in close proximity to passengers, it creates a risk factor during a crash.
There are more subtleties involved, but these are the primary considerations. I invite the experts here to weigh in with more details.