Earlier quoted context omitted.
With "Swarm", do you mean Docker Swarm? Why has it "fizzled"? The way I learned it in Bret Fisher's Udemy course, Swarm is very much relevant, and will be supported indefinitely. It seems to be a much simpler version of Kubernetes. It has both composition in YAML files (i.e. all your containers together) and the distribution over nodes. What else do you need before you hit corporation-scale requirements?
A little off topic but why do these orchestration tools always prefer to use YAML as I really feel it a harder to understand format than JSON or better TOML and it's the only thing that I don't like about Ansible. I see ruby kind of uses YAML often but are people comfortable editing YAML files? I always have to look up how to do arrays and such when I edit them once in a while.
Anything new needs a certain amount of sustained practice before you get the hang of it. I think I had to learn regex like four times before it stuck. I haven’t hit that point with TOML yet so I avoid it.
I’d suggest using the deeper indentation style where hyphens for arrays are also indented two spaces under the parent element. Like anything use a linter that enforces unambiguous indentation.
I prefer YAML for human-writeable config because JSON is just more typing and more finicky. The auto-typing of numbers and booleans in YAML is a pretty damn sharp edge though and I wish they’d solved that some other way.