Excellent deep dive. The uevent/netlink path is one of those things every Linux developer should understand but few actually trace through.

One thing worth adding: on embedded systems (ARM SBCs, Jetson boards), hotplug behavior can be surprisingly different from x86. Some device tree overlays don't fire proper uevents, and you end up polling sysfs as a fallback. The kernel's device model assumes a level of firmware cooperation that embedded vendors don't always provide.

The kobject lifecycle diagram alone makes this worth bookmarking.