The fastest route to cultural relevance is historical connectedness. According to C. S. Lewis, the more up to date a book is, the sooner it goes out of date. The same could be said of music; the truly classic will endure, and the trendy will be replace by the next flavor of the month. As one who plans and leads in congregational singing, I would like the majority of my emphasis to lie on the former. "A Mighty Fortress" will most certainly outlast "Lord I Lift Your Name on High." Some might argue it already has.
Does anybody notice that a significantly unique new genre of music hasn't been invented in 15 years? I'm sure there's some small niche or scholarly "progress" I'm overlooking in the field of "new music," but I'm talking about the repertoire of the general public. 75 years ago society stood on the brink of an unparalleled proliferation of musical styles, catalyzed by developments in music technology and the ensuing instrumentation. But for the moment, it seems to have settled. Here's hoping that the lull will drive us back in time as we search for aural inspiration.
So what will church music look like in 50 years? If you are a high church episcopalian, it will probably look remarkably similar to the way its been for the last 400 years. If you're a low-church evangelical, one can only hope it becomes less cliche, mundane, and driven by a secular industry. I think there's something to be said for a surge of upcoming innovation through bizarre combination of instruments. Michael Gungor is just the tip of the iceberg for this, and a resurgence of folk style music in many Reformed churches may be the predecessor (that got some of us to take out our mandolins and dust them off).
In closing, here's a stab in the dark: Expect to see some of this in Christian ritual before the mid-century mark!