The only possible connection I could see for them to bring the Wizard of Oz into the story doesn’t seem to make sense at this point in the show. The Wizard of Oz ended up being a fraud. After all that time Dorothy, the Scarecrow, the Tinman, and Lion were skipping down the Yellow Brick Road the Wizard of Oz ended up being just some normal guy who who told them all that they already possessed everything they needed to fulfill their destiny. And after talking to this wise old fraud Dorothy realized that she didn’t need to go looking for adventure because it was right there in her own backyard. It seems as if at this point in the series Emma has yet to discover who she really is or what her role is supposed to be so I don’t see her needing someone to give her advice that she already possesses everything she needs to fulfill her destiny. And Emma didn’t go off looking for adventure, Henry went and got her. Maybe if at some point she feels like she isn’t up for the task, or something and decides to run away I could see them bringing in the Wizard of Oz storyline but it just doesn’t seem to fit here. Maybe the dwarves can double as munchkins.