Board Thread:Show-Related Questions and Answers/@comment-25491743-20170410132437/@comment-26159109-20170410160541

In my opinion, there was nothing specific in the minds of the writers when they wrote that line in the pilot. I don't even think they would have done something with it if people hadn't asked them about it.

When Rumple said it, I don't think that they intended for the final battle to be with the black fairy, it just that she is the final big bad of the "current storyline" with all the main cast before the show either gets cancelled or rebooted. If the actors had continued with season 7, the final battle would have been with the big bad of season 7B.