Modern styles of liturgical music. Inherent problems or problems merely in the application?

Speaking of music after the Council...

Fr. George Rutler is always quite vocal about his thoughts on state of Catholic hymnology. He and others have been very critical of modern hymns either for their theology, for being too sentimentalist, etc. I think Fr. Rutler and others are right on the money in this regard.

Obviously as well the restoration of Gregorian chant is a big deal from a conciliar perspective, from the perspective of the post-conciliar popes, and in general as a Latin tradition. It needs to be significantly reclaimed into day to day parish life.

This leads me into another point. When considering the place (and production) of modern liturgical music, there are some matters that I find quite clear (such as those Fr. Rutler mentions, or such as the restoration of Gregorian chant) while there are other questions which I find less clear and struggle to find what I think a reasonable answer.

There was allowance in the Conciliar decree for some modern forms of music in addition to these forms. How might some of you on here see this being properly manifested?

What direction ought modern Catholic composers go? In terms of theology, I think this is relatively clear. The texts must present sound Catholic theology. Moreover, don't create pieces which are ultimately anthropocentric. For Mass settings, follow the liturgical texts. Plain and simple.

Stylistically, however, I do not, I confess, find it as easy to reconcile how some modern music might build upon the existing musical tradition of the Church. I can understand how that might be manifest in terms of an English version of Gregorian chant or Polyphony, akin to what John Rutter has done for the Anglicans, or what Byrd and Tallis accomplished under Elizabeth. I can also forsee how a further development in addition to this can employ the basic principles as such, as for example Anglican chant as they use at the singing of psalms which is a variant on chant and polyphony. I think all these things are desirable and to be encouraged -- though always with the understanding that this should not exclude and replace Gregorian chant.

But what about the use of non-traditional instruments like guitar? Or the praise and worship style of music? None of these are my thing personally, but I am hesitant to completely write them off as unsuited to the liturgy since I am not certain the Church would necessarily do so. I think as they are often employed these past few decades, it doesn't work with regards the spirit of the liturgy. But is this an inherent limitation, or rather just a limitation as the result of not having the best music, or not having given it that organic link with our tradition? Can the latter be done?

The question then, can, and if so how, can the latter be brought into unison with character and spirit of the liturgy, as well as the traditional musical patrimony of the Church? Can it?

No doubt this will be a controversial subject. I am bringing it to the readers of this blog for debate and discussion. The main thing is this, let's set aside personal taste (as I'm sure most of us wouldn't shed any tears if we never heard a guitar in church again) and consider this from the aspect of liturgical theology and how music ought to relate to that and the mind of the Church and Christ.