Doing some preparation for teaching a course on Christianity in Australian Society, I have been going back over some reading on ecclesiology, paying attention to one of the few mainstream theologians who has made this a major concern in framing his work.
The Canadian theologian Douglas John Hall has paid continuing attention throughout his career to the cultural disestablishment of Christianity in North America as opposed to the legal disestablishment of the churches in Europe. He combines this with attention to Luther's "theology of the cross" as opposed to a theology of glory. All this makes for an astringent theology that takes a clear stand against both liberalism and fundamentalism.
For a couple of articles online see: An Awkward Church
For an introduction to Hall's theological stance see The Cross in our Context: Jesus and the Suffering World (Fortress Press). What is curious is that he betrays no real awareness of the anabaptist tradition and history or its relevance for his argument.
Still like Stuart Murray in PostChristendom: Church and Mission in a Strange New World he regards the movement beyond Christendom as an opportunity to be rejoiced in rather than an occasion for lament.