Along these lines, a series of not quite evangelical but ardent Christian churches have collapsed in my area in recent years. A lot of them combined into a kind of mega-church, which does quite well. It originally considered itself Baptist but has switched to nondenominational to accommodate the increasing numbers of outside Christian sects.
Obviously they don't have TV broadcasts or anything, but the church gives off an air of profundity in its size. But usually lost in that aura is the fact that numerous churches utterly failed to give rise to it. Perhaps its numbers have swelled some since its inception because a collective effort can be stronger than many smaller ones. But the total numbers of people attending from the area has dwindled significantly, compared to when the numerous smaller churches were all thriving. It's a false sense of size.
Clearly this only amounts to a case study, and not even that (more like an anecdote). But it makes the predictions and conclusions of the article at least slightly more plausible, since it has happened already in at least one place.
And to qualify the predictions, the number of "census" Christians (of any sect) seems more stable, but the active, attending people do seem to have decreased some. At least from my viewpoint.
....
I honestly hope the trend continues. Not because I harbor ill-will toward religion, but simply out of curiosity. The general trend in civilization through the centuries has been toward secularism and away from hardcore religion. And I personally don't think it's a coincidence that we're as aware of the world around us as we've ever been in history, and that despite the evil that will always exist in the world, civilized nations are as humane as any have been in recorded history. The link can obviously be traced to other causes, and I state such a theory only as opinion, but I personally believe that this correlation does in fact have enough merit to justify some causation between the two.