Personally, I think it’s Neal who will be the reverse Tin Man. His motivation is his love for Emma and Henry and Rumple. The Tin Man thought he didn’t have a heart but of course he was the most emotional of the three. And, in the movie at least, the placebo the wizard gave the Tin Man was a heart watch. I will admit this is stretchy but it’s possible the Swan Pendant, last seen in Manhattan in the bar scene, is Neal’s totem and that’s what Zelena takes.
I like that – I forgot about the swan pendant. Now that you mention it, it does remind me a lot of the watch in the movie.