In his letter to the bishops of the world, Pope Francis also says a few things about the Post-Vatican II Mass, but not very much. But what His Holiness says is important and this sums it up very well:
At the same time, I(Pope Francis) ask you to be vigilant in ensuring that every liturgy be celebrated with decorum and fidelity to the liturgical books promulgated after Vatican Council II, without the eccentricities that can easily degenerate into abuses. Seminarians and new priests should be formed in the faithful observance of the prescriptions of the Missal and liturgical books, in which is reflected the liturgical reform willed by Vatican Council II.
I would have also added to the list of seminarians and new priests, old priests too should be faithful to observe the prescriptions of the post-Vatican II Roman Missal. They are the greater problem!
Pope Francis manner of celebrating the Mass at the Vatican is sober and without an exaggerated experience of His Holiness' personality added to it. He follows the rubrics for the most part and has lengthy elevations.
Pope Francis has also encouraged popular devotions especially adoration and Benediction of the Most Blessed Sacrament.
Does rigid unity, though, mean that the post Vatican II Mass cannot be celebrated in Latin? It cannot be celebrated ad orientem and it cannot be allowed for communicants to kneel for Holy Communion?
And does it mean that an organic development of the post Vatican II Mass does not foresee what the Ordinariate's Divine Worship, the Missal allows for the post-Vatican II Liturgy they celebrate, meaning Prayers at the Foot of the Altar, the older form of the Offertory Prayers and other customs associated with the pre-Vatican II Mass such as ad orientem and kneeling for Holy Communion at the altar railing?