The two remaining bishops are stretched thin. SSPX Faithful need bishops they can trust to confirm their children, and ordain priests theologically formed in Tradition. If you do not allow this, they will still go forward with it. 1988 all over again. A major setback on relations between the Society, the bishops, and the Vatican. You and your predecessor have already made it crystal clear the SSPX is not in schism. Also, maybe you could just go ahead and give full canonical regularization. :)