Oda likes parallels, so tag team vs Imu is likely to repeat imo.
And then, as people already mentioned, we can get Luffy vs BB Naruto-style, which is not ideal, but as to me BB is a more interesting character, I would prefer him to be the final villain.
I would actually enjoy Imu being defeated due to teamwork, so maybe it's not just Luffy & BB, but also Buggy, admirals, etc, kinda everyone against Imu, with Luffy & BB being the last ones standing like Roger & Garp now.