I think it comes down to Vegapunk's speech about different ideologies.
Just like Elbaph views Nika as either a liberator, or a destroyer.
Luffy and Teach, despite going both against Imu's idea of controlling the world, are opposite sides of a coin.
Teach apparently wants to control it himself.
Luffy doesn't want to control.
So, there 2 will have to clash for the One Piece, due to the fact that, once the One Piece is claimed, the whole world will enter a huge war (that will culminate with the fight against Imu).
So that's why I believe It's Luffy vs Teach for the One Piece, then the war against Imu.
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Also, Rayleigh said they learned about the Void Century during their travels. So, despite finding the OP, they weren't able to claim it. So we might find the Rio Poneglyph before the OP.