Benedict XVI had previously touched upon the subjects of adding new saints into the old Missal, the new body of prefaces in his explanatory letter that accompanied Summorum Pontificum. This was repeated in Universae Ecclesiae and, according to Sandro Magister's Chiesa, a commission was established in 2010 to look into the matter. The rumor mill is running in over drive (among certain circles) that a text of an "updated" Tridentine missal is waiting in the wings for publication. Of course, Benedict XVI revised the old Missal shortly after the publication of Summorum Pontificum; Benedict's freshly composed intercession for the Jews is found in the newly printed editions of the 1962 Missale Romanum.
Further "updates" or changes of the old Missal should be expected. Whether or not they are warranted so soon after Summorum Pontiificum is debatable. Many proponents of the old liturgy are still feeling somewhat raw over a thirty seven year struggle and are unsure of old liturgy's security. One can argue it would be best to leave the old liturgy be for sometime yet. However, it must be noted that the old liturgy was on the precipice of development prior to the Council. The sound scholarship of many luminaries in the original liturgical movement (most clearly demonstrated in their editing of hand missals) had shown the points of entry for a superior celebration of the old missal and areas of the old liturgy that were themselves avenues for development. All of this was subsequently jettisoned when the Missale Romanum of Paul VI was promulgated.Yet, development was near. Some would even say, in light of Pius XII's reform of the Easter vigil, development had been set in motion and it was progressing - with due reverence for the old liturgy. Indeed, if you examine the writings of the original luminaries of the liturgical movement, you'll be hard pressed to find anyone who would call for a new form or order of the Roman liturgy. All of them had a most pronounced reverence for the "Tridetine" liturgy saw so much potential in it.
The subject of developing or updating the "Tridetine" missal is being discussed by members of a curial commission. It is in the authority of the curia to discuss such matters. However, it is wise to remember that the giants of liturgical scholarship and theology from the last century were not an academic or curial think tank. They produced their work based upon concrete observations on the ground, without rampant experimentation. The Tridentine liturgy needs to develop. The climate of our current context still produces a reaction to freeze the traditional Missale Romanum in place at the edition published in 1962. Such an attitude would render the traditional Roman liturgy as little more than an antique curiosity. However, the old liturgy must develop on its own terms. I have long since excepted that we will likely not recapture the lightning in the bottle that electrified the original liturgical movement. That moment in history has passed and ecclesiastical authority squander the opportunities it presented. Rather than be cultivated, the fruits of the early 20th century liturgical movement were allowed to rot in the field and, barring the successful invention of time travel, that moment will not be experienced again. If the "Tridentine" Missale Romanum, that is, the essentially Gregorian Missale Romanum, undergoes any sort of updating, I hope it is with substantial input from persons or groups who celebrate this liturgy frequently.
By my reading of things, it has been a given that the new prefaces and saints would be introduced to the Gregorian liturgy, if not in fact some alignment with the Calendar and Lectionary. As I wrote in a previous entry, "two forms, one rite" is not a sustainable solution. Any updating of the "Tridentine" Missal will likely prove to be a move to bring the normal celebration of the Catholic liturgy back into the continuum of liturgical tradition. It would be the first step in a gradual process by which the Missal and liturgy of Paul VI is rendered obsolete without having to make a public about-face and formally abolish the work commissioned by another pontiff. While I do contend that the Pauline liturgy can be executed in such a way so as to keep it in the ancient liturgical tradition, the Pauline Missal is so impoverished of liturgical and ritual expression that a pedestrian liturgy is almost inevitable if a church or chapel does not possess a well trained group focused on reconnecting the modern Roman liturgy with the ancient manner and ethos of celebration. Typically, one has to look in monasteries for this. Nevertheless, it can and should be done.
For the moment, all discussion remains speculation. There is a commission established to study the issue and it has been in existence since 2010, verified by way of entry in the Acta Apostola Sedes. We do not know anything more than that.