Stan, you probably could use metal, but he glue choice would be what it is for metal to wood in a high stress situation and it would be hard to "make it disappear" after finishing. The wood splines provide excellent glue surface in a way that's very supportive of the need with tiny enough flex to be resilient and once contoured and refinished, they are "gone" from view. And there's that tone thing. Wood will likely have less impact on sound than metal would in this situation.
Carbon fiber would be another alternative, but it's generally used in the longer portion of necks when extra stiffness is required, not for a repair like this.
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The most expensive tool is the one you buy "cheaply" and often...