Here’s how I think it’s gonna play out: Oda will use these first few chapters to set up and establish what different groups are currently doing. We’ve already know that the Revolutionary Army is at Kamabakka Kingdom and they are rallying their forces together to wage war against the Celestial Dragons.
We also know that several sovereigns – some of whom have beef with each other (Wapol with Dalton and Vivi) – are making their way to Mariejois as well. Additionally Oda’s set up some tension between the CP0, Sakazuki and the Gorosei, with CP0 going over the latter’s heads back in Dressrosa, this can lead to some possible conflict.
Oda will possibly use the next few chapters to further establish the current position of varying groups and factions, but we won’t be shown any progress until much later. The arc will then proceed as can be expected – with a large amount of exposition on current world affairs, on the true history, and much more.
All of this will come to a head at the very end of the Reverie arc, when all these factions will come together and act as a prelude for what’s about to happen. At this point, Oda will cut over to Wano.
Now the reason why I think Oda put the Reverie arc before Wano is because news of what happens at the Reverie won’t reach our characters – and by extension, the audience – until the arc finishes. Oda’s established that Wano is cut off from the rest of the world, that even the World Government has no affiliations with them whatsoever. So there won’t be any newspapers or outside intel that would let us or the characters know of what’s happening. I think Oda will take full advantage of this isolationist country to create the ultimate form of suspense and intrigue as to what really happened at Reverie.
*Theory by sarmadqt