Perhaps screens and televised images are what the Pope has in mind here, in the 2007 Apostolic Exhortation Sacramentum Caritatis
vatican.va/holy_father/benedict_xvi/apost_exhortations/documents/hf_ben-xvi_exh_20070222_sacramentum-caritatis_en.html :
“**Large-scale concelebrations **
61. The Synod considered the quality of participation in the case of large-scale celebrations held on special occasions and involving not only a great number of the lay faithful, but also many concelebrating priests. (181) On the one hand, it is easy to appreciate the importance of these moments, especially when the Bishop himself celebrates, surrounded by his presbyterate and by the deacons. On the other hand, it is not always easy in such cases to give clear expression to the unity of the presbyterate, especially during the Eucharistic Prayer and the distribution of Holy Communion. Efforts need to be made lest these largescale concelebrations lose their proper focus.
This can be done by proper coordination and by arranging the place of worship so that priests and lay faithful are truly able to participate fully. It should be kept in mind, however, that here we are speaking of exceptional concelebrations, limited to extraordinary situations.”
Perhaps what he means is that for Mass at World Youth Day it makes sense to have a big screen with televised images so people can follow what is happening. But with the last sentence he is highlighting that such approaches are exceptional, to deal with exceptional situations.
The General Instruction of the Roman Missal does not mention a screen. But it does mention other things that should be central, or the focus of attention. For example, GIRM approved for the USA, which can be accessed from
romanrite.com/girm.html :
“296. The altar on which the Sacrifice of the Cross is made present under sacramental signs is also the table of the Lord to which the People of God is called together to participate in the Mass, as well as the
center of the thanksgiving that is accomplished through the Eucharist.”
“*The Ambo *
309. The dignity of the word of God requires that the church have a place that is suitable for the proclamation of the word and toward which the attention of the whole congregation of the faithful naturally turns during the Liturgy of the Word.”
“310. The chair of the priest celebrant must signify his office of presiding over the gathering and of directing the prayer. Thus the best place for the chair is in a position facing the people at the head of the sanctuary, unless the design of the building or other circumstances impede this …”.
“314. In accordance with the structure of each church and legitimate local customs, the Most Blessed Sacrament should be reserved in a tabernacle in a part of the church that is truly noble,
prominent, readily visible, beautifully decorated, and suitable for prayer.”
So a concern with a screen is that is would tend to be a distraction from these elements which are described as important.