Well, what if the quadruplets were the cheap engines?
Could totally change the equation, especially if there weren't somewhat "off-the-shelf" larger and smaller engines.
If you look at this article, it suggests 10-20% of DOC is engines. If you make that more complex and add 1 pp to save 1% in fuel, you're probably going backward.
I scanned the article but not sure what "10-20% of DOC" means. Is that cost of engine purchase and mx? Engine's contributions to fuel burn (through parasite drag and weight)? Engine's knock-on effects on overall frame size/expense, compared to a towed glider?
I'm sure it doesn't include not the towed glider comparative hypo, but unless an analysis accounts for the system-level impact of my proposal's claimed (from first principles only) negative delta to fin size, it would be incomplete.
Re complexity - this might be repeating myself but we have to disaggregate administrative and technical complexity. Compared to a normal quad, the proposal should reduce technical complexity: you have to mount/fuel/maintain four engines regardless and I'm just turning two of those engines into simpler, more robust NB types rather than the fine-tuned thoroughbreds mounted on WB's. On the tech side, there should be less complexity. Administratively, yes, it's more complex. But with the shift from labor to LLP within the mx cost burden (a shift that wasn't as marked for the 717 discussed in your doc, btw), the administrative/labor issues are less salient. Engine mx in total doesn't exceed 10% of DOC, afaics. Given a 2:1 ratio of parts to labor/admin within engine mx (~3% DOC for labor), you'd need a transformative adminstrative quandary for my layout to cause a 1% DOC delta.
Where's Lightsaber, I'd be curious for his take on the topic.
IIRC I've pushed this proposal at him a couple times and he either thinks it's too dumb for his time or has responded and I'm too dumb to understand.