There has been discussion recently of the appropriateness of celebrating Mass with a large number of the faithful and with large numbers of concelebrants. The terms of some of this discussion - should there be a maximum number of concelebrants allowed is one question being asked - seem to be similar to those of the discussions in the Consilium established to implement the Liturgical changes after the Second Vatican Council. Which is interesting in itself!
My experience at the Eucharistic Congress prompts two contrasting thoughts on this matter. Apart from the closing Mass Statio Orbis, Mass each day was celebrated in the "Coliseo Pepsi" on the conference site (the organisers re-branded some of the other buildings on the site for the duration of the Congress but do not seem to have succeeded in overcoming the Pepsi brand!) . The Coliseo is rather like a small, indoor sports stadium, able to seat something like 15 000 people or so. The seating arrangements are very much like you would find at a football ground or sports stadium, with access walk ways behind the seating area. You enter your seat through a tunnel from these walk ways, and then climb steps to your row.
How effectively can you "pray" the liturgy in this environment? My experience would give a positive answer. By an effective use of lighting and a sound system, and screens mounted above the arena that can be seen from the upper parts of the stands, a good focus was achieved on the sanctuary/altar area. I only realised half way through the opening Mass just how much I had focussed only onto the sanctuary/altar area - in a kind of orientation towards an "internal east" achieved in a most unexpected way. That I was not distracted by those around me also suggests that they were well focussed and attentive. However, people seated in more remote or higher parts of the stadium might have found it more difficult to achieve this focus and attention. (An ability to follow both French and English was also an advantage to my participation. )
At communion, people had to leave their seats, descend or ascend steps to the tunnels and go out into the walk ways to receive. By stint of good arrangements of, and sufficient numbers of priests, to distribute communion; and by calm, efficient ushering this was managed in total silence. The opening Mass was a bit muddled as people had not got used to the routine, but after that it just got better and better. One could receive communion in a very recollected manner, and make a thanksgiving as you waited to re-enter and return to your seat. (I had a very good experience in this regard - there might have been areas of the stadium where things were not managed so well, but I am under the impression that my experience was typical.) And every day there were numbers of people who knelt down in the stands near me for the Consecration, despite the difficulty of doing so.
The less satisfactory aspect - and I say this without any real thoughts as to how the difficulties could have been resolved - had to do with the consecration of hosts/wine placed on tables among the concelebrating bishops around the sanctuary/altar area rather than on the altar itself. One almost wondered whether the consecrating intention of the concelebrating bishops and priests "by-passed" in some way these hosts/wine as it was directed towards the main altar. Significant numbers of the concelebrating priests were in defined sections of the stands rather than near the altar, too. I became more uncomfortable with this aspect as the week progressed, though I could not think of any other way of doing things.
Possible solutions? You could use large numbers of hosts consecrated at earlier Masses to distribute Communion to the faithful - not ideal, but then neither is the situation described above. You could also limit the number of concelebrants, thereby allowing sufficient hosts to be placed on the main altar and removing the need for additional tables.
In practice, I think the Congress organisers struck a balance between being practical and respecting what one might call "principles"; I would not want to be seen as launching a major criticism of them. My experience suggests that it is possible to arrange large celebrations in a way that is prayerful and reverent for the faithful, and that, for an event such as a Eucharistic Congress, this is entirely appropriate. However, the question of the numbers and location of concelebrants is still a question needing a more defined answer.
POSTSCRIPT: As I finish writing this, the question occurs to me as to whether the question of "actual participation" (in the language of Vatican II) is not essentially the same as the question of an "internal east" (in the language of Joseph Ratzinger/Benedict XVI).