Here, a reiteration of Church teaching on the role of the pope:
Vatican Council II, when it described the catholicity of the People of God, recalled that “within the ecclesial communion” there exist the particular Churches which enjoy their proper traditions, without prejudice to the primacy of the Chair of Peter who presides over the universal communion of charity, guarantees the legitimate diversity and together ensures that the particular not only does not injure the universal but above all serves it”. [Cfr. Lumen Gentium 13]
Followed by the urging of bishops to unite to oversee the liturgy in their respective dioceses:
While, in the exercise of my ministry in service of unity, I take the decision to suspend the faculty granted by my Predecessors, I ask you to share with me this burden as a form of participation in the solicitude for the whole Church proper to the Bishops. In the Motu proprio I have desired to affirm that it is up to the Bishop, as moderator, promoter, and guardian of the liturgical life of the Church of which he is the principle of unity, to regulate the liturgical celebrations.
Ponder that word, regulate. Latin in origin. Suggests something along the lines of, well, a straight edge or ruler, a guidance applying existing law to particular situations in real life.
It is up to you to authorize in your Churches, as local Ordinaries, the use of the Missale Romanum of 1962, applying the norms of the present Motu proprio. It is up to you to proceed in such a way as to return to a unitary form of celebration, and to determine case by case the reality of the groups which celebrate with this Missale Romanum.
The suggestion here is that the local bishop will guide the movement of the people toward the modern Roman Missal. How long might that take? I imagine in many places that don’t currently celebrate by the 1962 Missal, the regulation will be immediate. In other places, the imposition of readings in the vernacular will be a challenge, and movement toward a unitary form will be gradual, perhaps halting, and likely take decades.
Here are the important links: