The longer we go without at least a Triglavian autopsy, the more certain it seems that the reason is that their biology and maybe even state of being is something … radical. They’re clearly knowledgeable about physics (singularity reactors, entropic disintegrators, stellar harvesting, etc.), but what if biology and infomorph engineering are their true strengths?
The main reason for the ban on mass-copying people-- multiple active clones of a single person-- is the eventually catastrophic psychology of the thing. People tend to develop a murderous obsession with eliminating their other selves. What if the “troika”-- I think that’s the term for a Triglavian tripartite person?-- exists as a way around this problem?
Depending on the approach, they might be able to manufacture or reabsorb troikas as needed. That could be the nature of the “flow.” The same volume of water can run broad and shallow, or narrow and deep. What’s on the surface may not say much of what is there. No need to worry about caring for unneeded population; no need to be troubled by losses; no need to defend precious individuals. What is needed is brought to the surface, in a configuration optimized for purpose both physically and mentally, then broken down and submerged again when its tasks are complete.
Even short of this: planetary populations might live underground, protected from lethal “weather” that would probably make most surface conditions nonsurvivable, and use the planet surfaces as gardens and laboratories for more exotic forms of bioengineering. Or they could live like modern astropolitans, never personally setting foot down a gravity well.
For that matter the bio-luminescent clouds we’ve seen in the Abyss could be biomass depositories or even farms, fields of life to be harvested to make whatever … even new Triglavian bodies.
Just because we can’t see it doesn’t mean it’s not there. And vast.