It´s borderline useless in it´s current state. Targeting enemy vassal kings may be the best option, to wekane a hostile empire, becuase it does not matter whether the king has problems with his vassals, or whether the emperor has problems with the king. But even then, it has very little use.
It could be made more useful with Conclave if the option existed to deliberately target the enemy´s council, making members of it "malcontent", or causing the council to become "discontent". Regrettably, nothing in this line is planned.