Apologies if I missed it earlier on this thread, but my vote for "upcoming number 1 problem" is lack of leadership.
Not Bethel strivers, not COs - in any organization of this size there will always be more than enough cynically ambitious guys trying to claw their way up.
I mean congregation-level leadership - elders & MS.
I have no data to back this up, but my observations are that there aren't nearly enough young guys who care to step up to become elders. It used to be that a typical elder body had a mix of guys from ages 30-ish to 60ish, maybe an old 80+ guy or 2.
Now, it seems like the age range is 55+ to 80+, with just a sprinkling of a few guys younger than that.
MS's are now primarily composed of limited-capacity 60+ guys who will never be elders, or 20- and 30- somethings who have little or no "depth". Most clearly have utterly 0 interest in being elders, and even if they are "drafted" to become elders, they won't be of much use to the org.
What happens in 10-20 years when the current crop of elders is either dead or greatly limited due to age, and the replacement pool just isn't there?
What with the trend of merging congregations, you'll have 140, 150, 160 publishers, to be "guided" by a 4 man BOE - 3 guys in their 80's and one soon-to-burn-out 40ish guy who will soon either quit or have a heart attack.
People will fade by the dozens, and there will be no one to "shepherd" them back.
This will start by the dozens of congregations, then 100's, then 1000s.
Congregation activity is, to a very large degree, driven by the enthusiasm of the elders. What happens when the primary concern of the elders is "where is the nearest bathroom" and "where did I leave my teeth?"
Stick around a bit - we're about to find out.