We are probably getting Gorosei, holy knights, Imu, Shanks, than Blackbeard and at last Cross Guild with Buggy, Croco and Mihawk in the end.
Luffy will need those guys to fight all the obstacles to get through the Empty Throne (think of WB crew helping him in Marineford because SH other than Zoro/Sanji are too weak) then Buggy will sneakly find a way sit on top of the throne with den den mushi broadcasted live.
I’m in the opinion Shanks is a villain, God Knight member and will their opponent.