I disagree about the curse not affecting other worlds. I think the dark curse is so dark that everyone will be affected. Storybrooke is where everyone from FTL went to. Yes, Jefferson was in Wonderland, but he still resided in FTL with his daughter so he and his daughter (along with everyone else from FTL) ended up in Storybrooke. But because Jefferson was trapped in Wonderland at the time of the curse (I’m just assuming) his house in SB that he’s trapped in represents the fact that he was trapped in Wonderland. But he’s still in SB because he lived in FTL.
In regards to August coming and going, no I don’t believe the Oz would have any powers (though it’d be nice). But I think each world has its own special mode of transporting between each world. For Wonderland, the hat is used to come and go. For the Land of Oz, the tornado storm is what got Dorothy out of Kansas. The hot-air balloon is what took the wizard of oz there (via storm). I think August’s motorcycle could be his “hot-air balloon” to go between worlds. For Neverland, idk… maybe you need special fairy dust is required to fly to each world. For Agrabah, perhaps the magic carpet is the only way in and out. I’m just making up stuff but I’m trying to make myself clear. I don’t think Jefferson’s hat is the only way to go to the other worlds.
As far as making the story too complicated, they definitely don’t have enough time this season to introduce us to the Land of Oz. But if we find out August is Oz, then I suspect a season finale cliffhanger that ends with the Land of Oz, hinting that they will spend an entire season explaining that world. And then season two ends with Captain Hook, which gives the entire third season to explain Neverland, and so on and so forth.
I know it’s a lot to take in and handle, but these writers can make anything work. We’ve seen it first-handed. With my theory, I’m not sure if everyone would still be in SB and only the flashbacks take place in the Land of Oz, or if a tornado comes sweeping through SB sending everyone over the rainbow, or even if everyone had multiple characters giving each their own identity in each world (chyeah right). However, Rumpel stated in the pilot that “the final battle will begin!”. I don’t think we have enough higher-power people for there to be a battle in SB. I think it has to include the other worlds or else this series won’t last long. They can’t just keep dragging it out for 8 or 9 seasons. Could you imagine if Emma still didn’t believe 8 years from now?! No way. There are already hints of her faith so something else, and I mean something big, needs to happen so that we know just how DARK this curse really is.
ps. They day August is Pinocchio is the day I become tinkerbell.