Doubler:
My premise was, BLC can make the empennage more effective. It artificially inflates tail-volume, and leads to efficiencies with less weight and drag.
However, if that BLC is reduced, or negated, you now have a conventional aircraft with very low tail-volume. That could make it a handful in an emergency due to phugoid oscillations/dutch roll/roll-coupling.
Some (a couple of friends of mine who have flown it) say the MD-11 has this issue for pitch control under normal circumstances. Adequate at cruise speed, but difficult at approach speeds.
An all-moving slab with FBW would probably be no heavier than a conventional Horizontal stab and elevator that has a trimmable jackscrew.
Vertical fin...maybe what you said. The practical side of BLC is how much does the ducting weigh and add to a conventional vertical stab?
And, through FBW, you could build a conventional fin where the rudder is a much bigger percentage of the total surface. Kind of achieving the same thing..don't make all of it move....just more of it.
And, I wasn't suggesting a retrofit to an existing design. It would have to be incorporated from the start.
Lockheed, McDonnell, Douglas, and Dornier all did major BLC tests or made actual production aircraft in the late 50s/early 60s. Some used blown upper surfaces, and at least one tried suction. Maintenance ended up being a major factor in not seeing widespread use. In particular, keeping tiny bleed pinholes free of dust, water, or ice was an unending challenge.
It's an interesting idea, but the pessimist in me says it probably won't work as well in actuality as it does on paper. Swing-wings suffered the same fate, and more recently, I was told the maintenance costs for fixing winglets on the 747-400 (cracks) cost more than the fuel they saved, and the little winglets on the A-320 had no effect at all on fuel efficiency!