Kevin Chadwick:
...
> Likely not much help but OpenBSD has static dev files and their
> hotplugd listens to events from the kernel on /dev/hotplug

You can have basically the same in linuxland, use a static /dev and
do (excerpt from https://git.busybox.net/busybox/tree/docs/mdev.txt):

Here's a typical code snippet from the init script:
[0] mount -t proc proc /proc
[1] mount -t sysfs sysfs /sys
[2] echo /sbin/mdev > /proc/sys/kernel/hotplug

and possible add mdev -s to fill /dev.

Regards,
/Karl Hammar