This is a good theory, and very possible. Jim often calls himself a lazy writer, who likes to reuse story elements and characters. And we haven't had a mention of the Barnabas Curse in quite a few books...
It also casts Murphy's death in a more meaningful context, which is (IMHO) both good and bad. The way Karrin died seemed really random and out-of-left-field, so tying it in to Nick's stratagem grounds it, helps it "make sense." It also means there was no way for Harry to save her,, and that might bring him some small comfort..
On the other hand... it also feels a bit like fridging Murphy for Dresden's detriment, making her a pawn in the battle between hero and villain, and I'm not sure that's a good thing. No matter how odd and out-of-place the death was, Murphy died trying to save others. It was still a hero's death, enough to qualify her to become an einherjar. I'm not sure if reframing it as a consequence of Nicodemus' schemes diminishes the impact of that.
We'll have to see how Mr. Butcher writes it. I suspect how it plays out will make a difference in how we view it.