That was a solid article. The "gradually, then suddenly" bit I get. We've probably gotten to the suddenly portion of a few things. I'd bet a lot of money on the continuing quicker hollowing out of the middle against the ends. You need the sacramental outpost. You need a central "branding" effort, at least if you pretend to be a confessional body you do. Anything between that is the stuff that gets disintermediated by technology and individualism.
Some of that suddenly factor is simply generational transfer, maybe most of it. The big box place was the boomer's response to nostalgia for the fullness of the church of their youth. And they would do anything to keep that - fog machines, zero theological content, etc. Believe, teach and confess was a deep secondary concern to "make me feel like the USA is still a Christian Nation". Nobody under 50 is fighting that battle.
The next wave of church-political elections really needs to be about one question: as we finally stop throwing money at stuff that can't be saved, how are we going to fashion a church that works in a technologically connected way?