In Dressrosa, the Revolutionary Army was investigating the weapons being sold by Doflamingo. They specifically said they wanted to find the source of these weapons.
Kind of a weird detail if there is no pay off. This investigation is going to take them to Wano. The source of the weapons. And when they arrive, they are gonna encounter the World Government.
And we are finally gonna see Monkey D. Dragon in action. Imagine Monkey D. Dragon fighting Kizaru or Green Bull. This could be a parallel to Sabaody. When Kizaru tried to kill Zoro, Rayleigh saved him.
The same way, when Kizaru tries to kill or arrest Luffy, Dragon saves him.
It also ties in with the core ideology of the Revolutionary Army. They liberate islands from the WG control. They could stop Wano from being annexed by the World Government.