For the record, this was a quote from Miller on Newsarama
"Miller, who came to comic books through his job as a writer for TV's Smallville, started at DC with a fill-in arc on Teen Titans before being announced as the writer on the new Batgirl series. Part of this summer's relaunch of all the "Bat" titles after the death of Bruce Wayne, Batgirl sets up former "Spoiler" Stephanie as the girl in the costume, but also include a supporting cast that includes former Batgirls Barbara Gordon and Cassandra Cain."
So, I think it is safe to say we'll see some character growth for both of them and some people are getting really angry at a setup that could fix some problems rather than create them. I think this is a good cast featuring three of my favorite batman-universe characters and I want to support.