Let's start with Babs. Even under the current creative staff they've referred to the fact that part of Babs' character is being a tech wiz. In her time as Oracle pre-N52, especially as her character developed, she was pretty much always the most talented computer and hacking related person period. Clearly, that doesn't need to be the case in the N52 but putting someone as Oracle above her feels like it would be the weirdest place to put a new Oracle.
It doesn't help that Babs in the current run is being written much closer to Steph than how Babs had been written for decades. I dunno, it just seems like a weird idea to bring her back as Batgirl only to then make her seem more like another Batgirl (The one she came back to replace, even!) and putting Frankie as Oracle would just further this. If it's going to be Babs as Batgirl then it should be Babs.
As for Frankie, well, right now she's her own character. Making her someone named Oracle feels like it would just be a link that doesn't seem to be needed, especially if it's just to help out Babs instead of as someone running/plugged into a huge information network for various groups of Important People. Her current role is fine, but the name just has pretty strong implications assigned to it and I'm not sure that's what's best right now.
Edit:
Of course, I'm perhaps sticking too much to pre-N52 canon, but that's part of my frustration. It seems like pretty much all the male Batfamily characters retain most of their history in N52 (Just compressed into comically short time spans) whereas all the women, outside of the two Batwomen if you want to count them, appear to have had much of their history ripped away. This fact bothers the hell out of me.
Edit 2:
I should also note that I say all this as someone that generally enjoyed Simone's Batgirl run and who has continued to pick up the current run weekly even if I'm not entirely sure my take on it yet.
