Just because there is area's to build on doesn't mean Kishi WILL do such a thing. Half of his story thus far has had holes, and he has yet to try to attempt to fill them. Kushina could quite possibly be one of those holes.Oh and by the way - It's quite narrow-minded to state that she holds no significance to the Naruto universe when you've been complaining about how little she has been mentioned throughout the series. There wouldn't be sufficient justification for such a claim. And before you come up with the same generic argument of "Then why hasn't she been mentioned earlier?" again, I'll point to where I said it's a wide open Universe with a lot land to build on.
If she was a strong Ninja it would have been said, just as Minato was. As you said in your first post it's up to speculation whether or not she appears in the series or not. I just gave my opinion, as Narrow-Minded as you claim it is, to why she won't appear in the series directly.