Is there any possibility that there will be a 4 final boss? Could Black Zetsu have been manipulating her?
Other Final Bosses Were
1. Juubito
2. Madara
3. Kaguya
Maybe Kaguya, personally, I believe it could be between Orochimaru (and for the obvious last battle) Sasuke, if he actually decides to consider Konoha on a neutral party or agreement.
Hopefully, I'm tired of the constant power ups and casualties to the story. Kishi should stick to what he has and finish it. I'm starting to think that the only reason he's stretching out Naruto is because Bleach and One Piece are still running.