I didn't really intend Ranette to become a kind of "Q" figure, providing Wax with a cool gun. I had written into the outline (once I added her) that he got a new Sterrion from her.
However, I wanted some more quirk to her character. Beyond that, I felt that one of the things this book should do is show the ways that Allomancy—and dealing with Allomancers—has entered the common consciousness of the world. It makes sense to build guns to deal with them, just as now we build guns specifically to deal with armor, or specific situations a combatant might find themselves in.
I felt that I wanted to integrate the Metallic Arts more into real society. You may notice, for instance, that I worked hard in this book to work Allomancy and metallurgy into the way that people speak. The metaphors they use, the way they see the world. A person who is up to no good is a "bad alloy." That sort of thing.
It would be possible to overdo this, of course, but I feel—looking back objectively at the original trilogy—that I didn't do enough of it. That's okay, because in the original trilogy Allomancy was something that you kept hidden, and the common people didn't know much about it. Feruchemy was an underground art, and only the Inquisitors knew of Hemalurgy.
Now however, at least two of the three are very common in society. I wanted to account for that. Building Vindication, the special Allomancer's gun, was a way to integrate the two halves of this book—the historical western and the fantasy.