Another significant detail (I give my opinion here purely as an individual) is the adherence to the Correctio of His Excellency Bishop Bernard Fellay, Superior of the Society of S Pius X, and of another priest of that Society.
What cheers me is that the Society is boldly standing up for the Gospel, as, indeed, one would expect the sons of Marcel Lefebvre to do ... and is also taking part in the life of the mainstream Church. It was never the intention of Archbishop Lefebvre that the Society should be a ghetto, even a tolerated ghetto, within the Church. That is why the Society so long (and so ultimately successfully) insisted that every priest of the Latin Church (and not only clergy of tolerated groups) must be known to possess the unfettered right to use the Old Mass.
I do not wish to be unjust to anybody ... and so I apologise if I have missed anything ... but I have not noticed that the Fraternity of S Peter, or the Institute of Christ the King, have been very public in the controversies which have followed the publication of Amoris laetitia. I would yield to no-one in my belief in the primacy of the Liturgy; but liturgical battles are not the only conflicts in which our Holy Father has in effect summoned us to Fight a Good Fight. Of course, responsible superiors have to bear in mind the damage which may be done to their institutions if they fall under the disfavour of heterodox, or just plain nervous, local ordinaries. But, surely, by virtue of our baptism, we still have some obligation to bear witness to the Gospel in the context of the Universal Church Militant.
Furthermore, the Correctio, based on the Magisterium of two millennia, is also willing to allude in its footnotes to the Magisterial teaching of Vatican II and of the later pontiffs, particularly the doughty Veritatis Splendor of S John Paul II (so disgracefully ignored in Amoris laetitia). The SSPX has been wary of the Magisterium of this period; understandably so. You do not need to remind me of the ambiguities in some documents; of the dangerous hares which were sent running in all sorts of directions. But for those of us in uncomplicated canonical relationships with the Holy See, such documents, in all their unevenness (including, in some cases, facile optimism and deliberately dishonest ambiguities), have been part of the currency in which we have had to do business. I again commend Aidan Nichols' fine and balanced The Council in Question, in which he admits the presence of an element which "occasions a genuine difficulty for orthodox Catholics". (We have just heard of the death of the admirable Brunero Gherardini, Canon Theologian of S Peter's in Rome, who wrote A much needed discussion, and whose Funeral was yesterday. C.A.P.D..)
I believe that acceptance of this situation ... that, perforce, we talk to each other in a theological dialect which has been influenced by Vatican II and the "Conciliar" popes ... is the substance of the doctrinal requirements which have been made of the SSPX. Bishop Fellay's participation in doing Theology within this general, if imperfect, context seems to me a sufficient and potent indication that the Society should be given a proper, and protected, and canonical status without further nitpicking.
It is a part of the Catholic Church; it has witnessed with great courage for nearly half century to the Faith once and forever delivered to the Saints. The time has come for it to be seen as an insider, not an outsider, in the momentous debates now happening within the Church Militant; the time for it to be heard.