It is a hard future to envision. Institutional churches are collapsing. I don't think that is for lack of faith or desire to reach out. In a way, the whole thing is simply built for a society and culture that is now in decline. University presidents, editors of publications, pastors of churches with schools, really anyone in charge of a substantial institution faces this issue.
What would be some actionable suggestions? "Get organized," or "Quit infighting and focus on the Gospel," or "Raise up servant leaders," are not actionable suggestions. I mean concrete proposals that can be said to have been completed within a certain timeline. What vote should be taken or change should be made such that five years from now we aren't in the same place only smaller?
Interesting. "...built for a society and culture that is now in decline..." follows a historical line that in Europe after the "fall of Rome", tribal/kingdom leaders identified a need for a unifying, civilizing element to lead peoples out of barbarism and chose Christianity to do that in order to establish basic civil order and make their people more governable. Only that.
I think God had something more to do with it, as all of us here including you and me also think (I hope). But this is an aside. The leaders of that multi-century era may have actually thought that was its purpose.
As to what are "actionable suggestions", I understand where you are coming from, looking for concrete proposals. As a life-long professional planner, I find that, simply, correct. However, we have actionable suggestions and concrete proposals that we enact every day. The concept of "immanence" (not the hackneyed SF or cultish versions) as defined by, among others, a student of "immanence" in socio-economic-cultural-ecological things, Adrian Ivakhiv (he is oftentimes a bit wacky, like me, but often has a few gems buried in his work, you have to pick through it with discernment) who found that "Philosophers of immanence, from Heraclitus and Nagarjuna to Spinoza, Whitehead, and Deleuze, find inspiration in the middle of things, the moment-to-moment movement of thought, awareness, connection, action, rather than in large, transcendent, ventriloquistic forces (such as ideologies, ultimate causes, or apocalyptic narratives)".
What's the point? It is "finding inspiration in the middle of things, including
action. We're in the middle of things, the most important of which is that God is doing the "action" through the Gospel. The Gospel and the accompanying actionable suggestions and concrete proposals in every book from Acts to Jude (at least) are everything we need.
I'm especially enthused by Jude v. 17+ff, "A Call to Persevere".
Please read Jude v. 17, pray over what it says, and "just do it".