Runit is finished at this point. It does what it says, and I haven't run into bugs.

Churn isn't a virtue.

Exactly this. Runit was designed to be simple and in simple software, at some point, there is just not much to improve.

Void Linux, "the BSD of Linux", uses runit and it has been fine since forever.

If there were any issues they would be worked on.

I’m glad to hear runit works fine for them.

I’m not so sure there isn’t any room for improvement though. In the related s6 project there is lot of discussions about adding new features that are beneficial for supporting a modern Linux distro.

As a datapoint of one, I've been using Void Linux for near a decade.

I haven't once been in a situation where I thought systemd would help. Granted, I don't run many custom services, but for what it does, runit does a great job. Something a bit more user friendly like s6 would be nice, but otherwise it stays out of my way and I don't think about it.

NixOS/Guix would be worthwhile switching to, but Void is comfortably simple.

Both runit and s6 are copies of daemontools which hasn't been updated since 2001. Try doing diffs of runit and s6 against daemontools. Are the differences are significant. What "improvements" were made.

Things can be built to last, including software. That so many programmers today are not building such things (possibly they are incapabale) does not change fact that some did so in the past (whether intionally or not), and some still can.

I’m not convinced that all development that has been made on runit/s6 over the years has been superfluous.