I think there is going to be a twist of some sort — there is obviously a connection between the frozen heart, the souls’ entrapment in UW, and the need for hopelessness. But so far, I have no idea how to put it all together. I can see how trapped souls might be powering the UW, and hopelessness prevents them from moving on. But wouldn’t the simple solution be to plop them all down into the River of Lost Souls (or whatever it’s called), and just call it a day? Trapped for all eternity, and voila, problem solved. No person, no problem. Or is Hades not able to do that? In the case of Hook, he didn’t seem to have any problem dunking him (outsourced to some sort of crane, but still). In the case of Gaston vs Rumple, he was setting up Gaston or Rumple to do it. But again, if he wanted a particular outcome, why not do it himself? I get it that he probably can’t drop a living person in the water of doom – some kind of limitation on his powers – so my only explanation was that he was really banking on Gaston getting the best of Rumple, but would have been satisfied with the opposite outcome because it fulfilled another function. I’m guessing in this case that quantity of souls in river of doom is in direct correlation with amount of general hopelessness in UW.
On the other hand, what would restarting his heart do, pragmatically, for Hades and UW? Clearly, Hades isn’t trapped in UW, but I wonder if his stopped heart is something that limits his powers? On the other hand, I wonder if a stopped heart might connect to immortality? What if Zeus was actually doing him a favor?