I was JUST thinking about Rumple’s agenda with the Dark Curse and the history of how it changed hands to try to understand it. So Rumple created it and and we don’t know when or why. Part of the curse requires the conjuror to contribute the heart of the thing he or she loves most – this leads me to believe that Rumple never intended to use it himself because he had already lost his wife and his son (don’t know if he had also lost Belle at this point). I can’t imagine him conjuring a curse that would require him to kill the person he loved the most since he was already in so much pain from losing people he loved.
So Rumple created the curse and at some point either gave it to the EQ or she took it from Rumple but she didn’t use it then for some reason. Why? For some reason she felt the need to either take it or ask for it but then decided not to use it. Instead she traded it with Maleficent for the Sleeping Curse. So did things get better for some reason so that she felt like she only needed the Sleeping Curse? Maleficent obviously thought the Dark Curse was dangerous and should never be used. EQ said that Maleficent was her only friend. So did Maleficent talk EQ into a trade to try to protect the Dark Curse from ever being used? And speaking of Maleficent, where is she in Storybrooke?
Then EQ decides that life has gone to pot again I guess and gets the Dark Curse back again. Now that I write it out this way it makes more sense when Rumple told EQ in his jail cell to hurry up and use the curse already. So I guess he could have been preparing for years for EQ to use the curse. He might not have even known that she traded it to Maleficent.
I still think there are too many holes in the backstories of EQ, Snow, and Rumple to be able to even come up with plausible theories on agendas. From Paley Fest it does sound like we are going to have enough of everything by the end of the season to at least understand what everyone’s motives could be.