SSPX is in no position to make demands. The door is open to them if they wish to return to the Church but the pope has no obligation to purport to bargain away the powers and authority of the papacy in order to reward illicit and excommunicated bishops, any more than Pope St. Pius V had the authority to bind his successors on prudential matters such as banning any changes of liturgy as he purported to do in Quo Primum.
Just a note - the language in "Quo Primum" was usual for pontifical documents of that time. It was never meant to impose an obligation on Pius' successors - he knew very well that he could do no such thing.
Look, the SSPX makes no "demands." It is Rome who came, hat in hand, to talk about "reconciliation". Of course the Society will obediently discuss anything at all with the Holy See, according to its wishes--but it will not compromise Tradition for the sake of getting along with this Pope or with any of his successors. It is the Pope who must first reconcile himself to Catholic Tradition--then all else will follow.