Yup. All that setup could and should have been done beforehand. But the fact that she was kicked out of her own team book by Tomasi, and Battle for the Cowl completely ignored her (not that she would have gotten GOOD characterization from it, but she wouldn't have been MIA for no good reason, at least) killed that possibility.
Well, it makes sense that you don't see it as a problem. Just as I don't feel the mistreatment of Cass destroys my enjoyment of Steph's solo as it exists. It's all about the character you are more invested in, and for me, it's Steph. (Also, it's called "Batgirl: Stephanie Brown" now in trade ).
That being said, the point of the book was clearly a Steph solo, though it has a LOT of Babs (at least for the first year).
Good parallel counterfactual there. The biggest problem with Steph in a series where Cass is actively functioning in the same general area is that she cannot compete on a sheer combat level, and thus there's going to be a constant pressure to be the same kind of Batgirl, or for people top wish for the better Batgirl.
And that's not what a Steph Batgirl series would need for Steph to become respected as Batgirl. Now, if your position is, as I know it is for many Cass fans, that Steph's natural place in the universe is as Cass's sidekick, then you have little desire to see Steph strike out on her own.
But I do.