Well, Cass getting her own series again would be the ideal, but my complaints would settle to a dull roar if it was Steph under the cowl. I don't THINK they'd put Babs in that costume, isn't half the appeal of her as Batgirl the visual of her lovely red hair flowing loose (and impractically) behind her? I can't imagine they'd waste the opportunity to exploit that iconic image.
Of course it could be a tease and the costume choice could have little to do with anything.