Apparently Pope Francis asked for this addition to the Calendar of the Ordinary Form because this Memoria was familiar to him, having been granted by indult to Argentina. In Magisterial terms, it goes back to the Allocution to the Council Fathers which Blessed Pope Paul VI made at the conclusion of the Third Session of Vatican II, when he formally proclaimed Mother of the Church as a title of our Blessed Lady (he did this after Conciliar liberals had shown recalcitrance towards this title*). The new propers now promulgated for this Memoria have, in the Office of Readings, part of Blessed Pope Paul's Allocution. Legem credendi lex statuat orandi. It's now Big Magisterium!
PF apparently likes this particular title of our Lady because he has used it several times since his election. But on 2 June 2013, when this pontificate had hardly started, a clerical columnist in one of our English Catholic Newspapers got in pre-emptively with his criticism and wrote "Pope Paul VI cheated and referred to Mary as Mother of the Church during one of his private documents during the Council" ... an engagingly cheerful and dashing dismissal of an act of Papal Primacy in the midst of an Ecumenical Council! But perhaps we should indeed follow this relaxed lead in our treatment of papal utterances. Is there anything wrong with light-heartedly calling a Pope a cheat? Surely not. This is just the sort of happy, friendly banter we need in a Church which has learned to avoid Rigidity. Lighten up, folks! And why on earth should we not dismiss a papal Allocution to an Ecumenical Council as a "private document"? I'm sure the time will soon come when "private documents" such as Laudato si and Amoris laetitia will have disappeared completely from Catholic consciousness.
Probably Vatican II itself will then be as highly regarded as, say, the Council of Vienne is now. Sub specie aeternitatis ...
Happily, Pope Benedict XVI (unknowingly) provided ways ahead for clergy who, like that columnist, intransigently dislike this title of our Lady or the important place PF has now given it in the Novus Ordo Calendar. On the Monday after Pentecost, blow the dust off your old pre-conciliar Altar Book and just celebrate the Extraordinary Form! Or ... if you have Ordinariate chums who, in the absence of an Ordinariate priest, ask you for an Ordinariate Mass on that day ... Bob's your Uncle!
I will publish the final part of this in a couple of days' time, and only then consider Comments.
*Over at NLM, the admirable Matthew Hazell has given illuminating extracts from the reactions of contemporary conciliar observers. Goodness me, HOW the poor sweet things did fume!