How do you know what kind of bankai Rukia has? I haven't read the manga, but honestly I'd be surprised if her (future) bankai is revealed even there. She's not captain level yet. I guess it would be possible she could achieve bankai already because she's as old as Renji, but Renji as always seemed more pressured and power hungry (ambitious) than Rukia, thus making quicker progress of larger steps possible.
The after credits part of this episode was bloody funny. Far better than the episode itself. While this filler arc didn't actually bother me at all, I'm not sorry it ended already, considering it seemed to be going down.