Where exactly they was hinted like that? I know that Gorosei carry Ancient Weapons names, which means opposite. They know everything about ancient time and World Cleansing.
Finding One Piece is not end game. You need to find One Piece to be able face Imu and Gorosei, it is simple as that.
Even saying more, you need to break Marines in Half with creating Sword to create a chance to defeat Gorosei and Imu.