I think there are two ways the new Rebirth Batgirl and the Birds of Prey could go:
1) Back to the traditional lineup of Batgirl, Black Canary and Huntress (plus one or two others). This is supported by John's statements yesterday mentioning them when talking about what made the original book work and with their images together in the announcement video. Also, DC has just recently released a new trade with the original Dixon stories and is following up with a second volume next week.
2) New "fresher" lineup of Batgirl, Black Canary, Frankie, Steph and Harper as shown on the cover of Batgirl #50.
I would, of course, prefer the original three. It worked so well and if it ain't broke, don't fix it. (But break it they continuously did by adding too many supporting members after Dinah left in the first run, adding lesser known characters in the second run, and I can't even figure out how they went so wrong with the New52, oy!)
But I have a feeling they'll go with the latter. I'm not currently reading Batgirl so I don't know how aggressively they're setting this up. But that cover just seems to predict it.
Of course whichever way they go I'll pick it up as long as Dinah's in it. Just curious to see how "legacy" the whole Rebirth initiative goes.