Do spokes exclusively fail in shear at the little hole through which they pass in the hub? To clarify, have you witnessed spoke failures in other areas?
Perhaps to material defects and thus excess tension causing necking, or shearing at the rim from a torque, or some other failure mechanism?
This question is purely academic. (And I would guess that necking is highly unlikely, hence why I say by defect, because these things can take very large tensile stresses as I understand it. Also, have you ever witnessed any severe radial loads that caused a spoke to buckle?)