It have been confirmed that Buggy is a Shichibukai which means there is only one Shichibukai left that we don't know who is and there probably going to be a new one to replace Doflamingo, so far the Shichibukai have had a opposite with the exception of Mihawk and Gecko Moria.
Law split people and buggy that splits himself.
Hancock that immobilize people by turning into stone and Doflamingo that can control their movement.
Kuma that repel things and Blackbeard that pull devil fruit users to him.
Crocodile which as hes best at a dry desert and jimbei that is at his best in the water.
So I assume that the last one we have'nt seen yet and the new one that is going to replace Doflamingo will have powers or theme that is the opposite of Mihawk and Moria, so what would their oppesite be? Moria suppresses his subordinate force them to do according to his will, so his replacement is maybe someone like Luffy that believe in his crew and don't force them to do anything against their will. ( well Nami, Ussop and Chopper don't like his ideas but still follow him ) What would Mihawks opposite be like?