After conferring the leadership of the Society of St. Pius X, it is likely this document will be signed as it will allow the SSPX to continue its measured and reasonable criticism of the Vatican Council Documents.
In the linked article below, Bishop Fellay describes a phone conversation he had with Cardinal Hoyos wherein the Cardinal admitted that +Fellay could have such reservations and level those criticisms while being Catholic at the same time.
Today, for the sake of objectivity, I must acknowledge that in the doctrinal preamble there is no clear-cut distinction between the inviolable dogmatic sphere and the pastoral sphere that is subject to discussion. The only thing that I can say, because it is part of the press release, is that this preamble contains “certain doctrinal principles and criteria for the interpretation of Catholic doctrine, which are necessary to ensure faithfulness to the Church’s Magisterium and to "sentire cum Ecclesia" [thinking with the Church]. At the same time, it leaves open to legitimate discussion the examination and theological explanation of individual expressions and formulations contained in the documents of Vatican Council II and of the later Magisterium.” There you have it; no more and no less.
Link to here...Dici