I thought about the person standing in fronrt of the Skyline. I mean I was convinced it was Bae, but after the information of this episode. Maybe it is Rumplestiltskin as normal human (Spinner), who is standing there, because when he cross the line he will be no Dark One, because magic can't come with him. Only the scarf, that he enchanted in Storybrook.
Or it is a reference what he will see by the seer. A glimpse of the future “The Skyline of the land without magic”
I hope we can see both flashbacks. I want to see Rumples past and Baes journey. After 3 weeks waiting it would be very nice of K&H.