There are overall tons of points which makes me think that the entire story of One Piece is going to roughly play out as the Skypiea Arc did.
– There are the Ancient Kingdoms forces (Shandians)
– There is Im = God Enel
– There are people (Skypieans) who are “good” but are actually controlled/brainwashed by God (Celestial Dragons/God Enel)
– There is the Ark Maxim of Enel (which is similar to Ark Noah)
– There is a promise from 400 years back that gets fulfilled (similar to JoyBoy’s promise from 900 years back?)
– Forgotten history, Void Century = forgetting that they were part of Jaya
– Lost Kingdom, Ancient Kingdom = Sky Island’s Upper Yard
– Impact dials are described as being forces that impacts the person “from the inside” exactly like the Advanced Armament Haki.
– There is a final survival match-up that happens in a cage similar to Dressrosa arc.
– There are paintings of ancient warrior fighting a multi-headed hydra, like Orochi in the ruins of Shandora.
– The “old” God is one of the fighting forces involved in the final battle (this is equivalent to the original rulers of the Ancient Kingdom)
– The promise was between the Shandora’s head, the warrior Kalgara, and Noland, i.e. two kings.
– Luffy satisfies the promise which is heard by the descendants of the Ancient Kingdom and Noland.
So overall, I think the way the final fight plays out in Skypiea is roughly how the final fight is going to play out between Luffy and Im.
*Theory by __tremb__
