My thinking is that he's somehow going to leverage the power that will be generated by the breaking of the curse to free himself from the curse of the Dark One. Or, hm. Since it seems to be important that Emma restore everyone's happy endings (or at least the happy endings of all the important people) before the curse can be broken, maybe he's counting on her to do the same in his case?

Granny vs. Gold would be an impressive match up. Like you said, she's wary of him, but I don't know that she's necessarily afraid of him. Interesting words would exchanged. Which reminds me of another theory that's been floating around, that Belle and Granny are one and the same.