I'm considering allowing Sound Constitution to be taken as an option in place of Talented (Choose One) when an Origin Path provides a duplicate Talent. This seems about as useful, and may allow - at most - two or three additional Wounds over what the character might be able to take normally. Does this seem like a reasonable and fair house rule?

It sounds pretty reasonable. Though If I were making a new character, I'd take Talented personally, they're hard to obtain naturally.

Yes most people can easily get Sound Constitution and I would rather have the +10 to a skill over one bonus wound. In fanct, very few Players in my DH or RT games have taken Sound Constitution (one guardsman and a Tech Priest being the exception) more than once.