powerman-overlay VS void-runit

AFAIK, There's nothing preventing someone from building a stage-3 snapshot for pure runit init. powerman-overlay appears to have some ebuilds that would support it. It would likely benefit from a custom profile. I have never seen such a snapshot yet, though.

It was merged in January but a release wasn't tagged until recently. I doubt anybody had systemd in mind when choosing the paths; the use of *.d names to describe directories that are "assembled" to form a cohesive configuration pre-dates systemd.

That's a neat change in the void-runit package! Unfortunately this not yet in the official runit-void package. The current version there does not have the shutdown.d folder, so currently I also don't see an easy way to handle this.

Did you edit https://github.com/void-linux/void-runit/blob/master/core-services/02-udev.sh with something like like mdevd -O 4 mdevd-coldplug? which initram if any?

By the way zzz is just a shell script. You can find it here: https://github.com/void-linux/void-runit/blob/master/zzz

and here is more bloated void-runit

Maybe this could be related: https://github.com/void-linux/void-runit/pull/81

Void Linux honors the cache file for boot-time imports. The pool holding any root will have already been imported by the initramfs, but other pools will not be imported by the initramfs unless automatic rootfs detection is used.

Runit has run levels. It scrapes the kernel command-line for a level that matches a service directory.