The topic is memory safety, not concurrency support, FWIW.

Lua would have been a good candidate: memory safe, coroutine to structure the code in a concurrent-ish way if needed, and you have a configuration file parser for free (just use Lua as the configuration language, it was its very first purpose after all).

> Ocaml parallelism/concurrency story was not that good

I wouldn't expect CPU-bound multithreading to be much of a concern in an init/rc system. And resource thriftiness and predictability would likely be a bigger concern.

While that would be amusing for sure, systemd's pid 1 is actually single threaded.

>Ocaml parallelism/concurrency story was not that good

OCaml concurrency is great, and Lwt [1] would be exactly what systemd need: run daemon and poll the answer concurrently.

Ada, C++ and D would have been another great choices.

[1] https://github.com/ocsigen/lwt

That's nice in theory, but where are all the people who know Ocaml to write it and contribute to it ? I might be clueless but I can't really name any significant projects written in it, which might imply something about the number of people using it and being able to work on and contribute to something as large and important as systemd.