I don't know that you can draw conclusion from people's experiences with other softwoods, as the species do vary a lot. White fir seems like it's really soft (very low janka, half that of mahogany), and very lightweight (again, half of honduras mahogany). The published modulus of elasticity is surprisingly high (higher than mahogany), which makes me suspicious.
I would say most of the time, not a lot of attention is paid to curing 2x4s properly, I would be worried about that. Myself, I would not use it for a neck, though I would consider it for a body core if I could be satisfied that it was dry and not going to want to move.
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