I actually still think we might get an alternate universe of these characters. So the flashbacks would be how that alternate universe came to our world, how these characters are different, the parallels between these characters and the ones we know, and what their motivations are. I can see Rumple still getting Regina or maybe Lucy’s mom to enact the dark curse to bring them here maybe because he knows that in this universe he has a family and wants to take over that life (parallel to finding Bae, maybe he does not even realize that Neal is not alive in this universe. Now how this would work or if we would find it interesting, I don’t know. I just don’t see A and E deliberately messing with the ending of Season 6 because they are scared that they would upset fans. If they did this the returning characters would still have to be very similar to the ones we know, but they could be interacting with different characters in different ways. Maybe Henry does not know he has a child because in this reality he does not but the Alternate Reality Henry does. I know probably not correct.
Personally I like the idea of alternate realities because that would free them up to reset the villains back to their most interesting setting and we can still keep the happy beginning for our characters. They could even have a peep hole or something to see into ‘our’ Storybrooke and see how happy their alternate selves are.
Manic crazy golden Rumple: “What do you mean I have a wife and children? I’m the Dark One!”
Revenge obsessed charming Hook: “I do like the blond.”
Evil quip-mistress Regina: “What the heck am I wearing?”