I'd be fine with there being two (or more) Batgirls, but I think with the old timescale asserting itself again, Babs should be well past being Batgirl by now, given that she's likely somewhere in her thirties. However, DC did some pretty good stuff with both Steph and Cass in the role, and they are shown as working reasonably well together most of the time, so I could live with that, but would prefer Steph as Spoiler and Cass as Batgirl if Black Bat/Blackbat (or her JL-Elite cover name Kasumi) isn't an option.