Let’s turn to what VL has to say about music:
40. Music and singing, which express the soul of people, have pride of place in the liturgy. And so singing must be promoted, in the first place singing the liturgical text, so that the voices of the faithful may be heard in the liturgical actions themselves. (SC 118; also 54, old GIRM 19)
Singing the Mass, not just singing at the Mass: excellent.
The note for this last section is supplemented by a nod to the people’s participation in Latin:
While allowing that “a suitable place be allotted to the language of the country” in the chants, “steps should be taken so that the faithful may also be able to say or sing together in Latin those parts of the ordinary of the Mass which pertain to them,” especially the Our Father.
Interesting that the Lord’s Prayer would be included in the Mass Ordinary; that’s not a traditional view of the piece.
As for the rest of the section, VL gives a nod to the local cultural traditions of music, and its suitability for the liturgy, citing Vatican II:
“In some parts of the world, especially mission lands, there are people who have their own musical traditions, and these play a great part in their religious and social life. Due importance is to be attached to their music and a suitable place given to it, not only in forming their attitude toward religion, but also in adapting worship to their native genius.” (SC 119)
The texts themselves are very important. It’s not just about Latin, or about cultivating cultural talent of composers and musicians:
It is important to note that a text which is sung is more deeply engraved in the memory than when it is read, which means that it is necessary to be demanding about the biblical and liturgical inspiration and the literary quality of texts which are meant to be sung.
Suitable material–not just that. But VL endorses what “can be made suitable,” implying that musical inculturation will try things, test things, reform and adjust things to make something work for the spiritual benefit of believers:
Musical forms, melodies and musical instruments could be used in divine worship as long as they “are suitable, or can be made suitable, for sacred use, and provided they are in accord with the dignity of the place of worship and truly contribute to the uplifting of the faithful.” (SC 120)
The citing of “melodies” is interesting here. That certainly would include something composed in the style of the culture. I’m not sure it wouldn’t preclude secular influences. A non-Christian religious melody adapted for the Mass–I would think that requires a very careful approach.
In the US, I’d think back to the 70’s. Using a few of the songs from Godspell seemed a decent approach, especially as some of Stephen Schwartz’s music was itself derived from hymnody and Christian devotion. But existing pop songs because they have a reference to Jesus? Please. Better to compose in the style of the music.