I don't think Steph has a big enough fanbase to carry her own book. If she had she would have been Robin longer than she was and wouldn't have been so casually killed off. The "Batgirl" title however will bring in curious readers though. Personally, the whole "Who is Batgirl" mystery to bump up out of the gate sales reminds me of movie studios that don't let reviewers see their movies in time for a Friday opening because they know it's a stinker.
This has nothing to do with Steph herself. Or even the quality of the book which will eventually become obvious but just in the way DC's rolled this out makes me think they were not as confident about the new Batgirl as they have publicly stated.