Board Thread:Spoilers!/@comment-3010035-20150701044944/@comment-24674051-20150706182052

Well, let's remember, back in Desperate Souls, that Rumple was a coward, and had sunk to the point of licking boots. Then, as soon as he became the dark one, he was the one inflicting pain. He was still a coward, hiding behind the mantle of the Dark One, but he was immediately powerful.

Emma has no cowardice issues (She's a born leader), she is powerful in her own right (We have yet to see just how powerful she is without the DO magic), And she KNEW what she was getting (or at least she thought she knew). I don't see it taking long for her to start flexing her new Dark Swan muscles. All the more reason that someone other than Emma maintain control of the Dagger. And Probably not Killian. I think either Mary Margaret or Regina would be the best candidates.