Why can't he be KotW without being PK? IMU is currently KotW without the One Piece treasure.
BB's combination of DFs will just become a danger nobody saw coming, which will allow BB to defeat & absorb IMU.
Meanwhile, Luffy's journey will get him the treasure, which will be used to stop BB.
King of Land vs King of Sea
Two Ds with similar yet opposite ideologies duking it out EOS, after the third outsider (IMU) has already been defeated by the side of the wronged Ds (Davies), who themselves need to be stopped before turning into something much worse--thus, by stopping this new, bigger threat, JB's will will also be fulfilled, bringing the world together as one.