I have to say, the whole neighbouring worlds theme is so reminiscent of parts of books in the Chronicles of Narnia, especially The Magician’s Nephew. The Hat is like The Wood Between the Worlds, with doors instead of pools of water. The Last Battle also makes mention of other worlds, at the end. Lucy sees that Narnia is actually ringed by a great chain of mountains, one of which is England. To this Mr Tumnus replies, “That country [England] and this country [Narnia] – all the real countries – are only spurs jutting out from the great mountains of Aslan. We have only to walk along the ridge, upward and inward, till it joins on.”
All this to say that I really hope Narnia is included in Once Upon a Time, and since Disney helped distribute the Narnia movies there might be hope yet!