To the posters suggesting this wouldn't work for Evangelicals, I absolutely agree. It's groups like Ultra-Orthodox Jews, orthodox Calvinists, Mormons that would be able to make this plan work. Evangelicals by their very nature aren't inclined to separate and their church structure would make it very difficult to do so even if they were inclined to be.
Not by their nature as Evangelicals - by their nature as part and parcel of American mainstream culture. To become a well-organized minority group with considerable minority influence, you'll first need to be a minority community, divorced from the majority culture.
Depending upon how exclusive one wants to be with the term Evangelical, it not difficult at all to define them a minority today. However, even with them being a minority, Evangelicals by their very nature cannot divorce from the majority culture, for to do so would be to abandon evangelism. That's the point that is being made here.
I think "minority" was not being used in the literal sense but in the cultural sense here-ie White evangelicals are essentially indistinguishable from the dominant culture of America.