Sociologist Mark Chaves, in Congregations in America, reports that the largest 10 percent of congregations contain about half of all churchgoers on an average Sunday.
Scott Thumma, the leading expert on megachurches, found that about 80% of them use electric guitar or bass and drums “always” in their services, and over 93% do so “often” or "always." Megachurch attenders are notably younger and have more kids than the mainline denominations do, so this preference is likely to multiply in coming generations.
Add to this that Roman Catholics, the nation's largest denomination, do not rely on organs.
The era of the church organ, which we think of as ancient, but is really less than two centuries old, may draw to a close in a generation or two.