Board Thread:Spoilers!/@comment-25582606-20150302140622/@comment-26211408-20150318205411

And I mean, Regina always expected Snow White to be pure all the time, so the curveball could be Snow and Charming, and how Snow's dark spot on her heart effects them.

Because of Snow and Charming lying and hiding secrets, the heart could be blackening to the point where one side is totally black, so one becomes evil and the other becomes good. Something along those lines.

I also like the idea that Regina could have the highest potential for goodness, though when Mal explained it, she stated that Emma had as great a potential for goodness as she had for darkness, which implies that Regina's potential for darkness isn't as great as Emma's. Since potentials are supposed to be equal and opposite potentials, I'm thinking Regina doesn't have as great a chance her potential of goodness as Emma.