Go back to Dressrosa. The Revolutionary Army was present in Dressrosa, due to their interest in the weapons Doflamingo was shipping. The weapons made by Kaido and Orochi . I think The Revolutionaries will trace the source of these weapons to Wano, and will arrive in Wano.
The World Government is using these weapons to cause wars in countries and then offering military assistance to these countries thereby making them depend on the World Government.
I’ve painted a scenario in my mind. It is kinda unlikely but really cool. Imagine. The war in Wano is over. Kaido is defeated/dead. Orochi is murdered, Big Mom is dead/defeated. Wano is free and the borders are opened. The heroes are down and out. But who arrives but CP-0 and maybe the Marines.
They see this as an opportunity to take out all these big troublesome Pirates out of the picture at the same time. Luffy, Kid, Law every single person is down for the count. If the Marines come, they would have Kizaru and maybe Fujitora/ Green Bull too. No one is in shape to take on the Marines. That’s when the Revolutionary Army arrives. All members from across the world. They had come for the weapons. But now they had a bigger situation at hand. Dragon fights the Admiral(s) and makes the Government retreat.
And then Dragon meets Luffy, as he mentioned after Enies Lobby, and has a father/son moment with him.
Vivi, as I said is with the Revolutionary Army up until now, and she reunites with the Straw Hats here.
From here, after obtaining the weapons, The Revolutionary Army leave to fight the World Government and retrieve Sabo.
Why Vivi and not Luffy is the reincarnation of Joy Boy
- I don’t think Oda would make it this obvious.
- It would fit in with the Gorosei perceiving Vivi and the Alabasta kingdom as traitors.
- It would break the typical shounen trope of “the boy from a prophecy”.
- She met Shirahoshi as well like Shyarly’s prophecy said at the expected time.
- Luffy is not the type of person to lead the world. Luffy will be the one who creates the dawn ( is D = Dawn ? ) and Vivi will lead the world forward.
- Im-sama IMO is trying to erase Vivi because I think he/she knows Vivi is a threat. He/she knows Vivi is important to change the future.
- Oden said that the borders of Wano need to be open to welcome Joy Boy. But Luffy is already in Wano and the borders are not yet open. So someone else ( Vivi IMO ) will be Joy Boy.
*Theory by letsgomina