From that perspective -- the perspective of systems which boot once, and boot again maybe next year if the UPS didn't keep them up when the power flickered, and the perspective of the systems where there are definitely not usb drives or random pieces of unknown crap plugged into user accessible ports, the idea of hotplug at all is the least of concerns, and the idea of boot time is laughable.
Essentially, it seems like systemd is chasing Windows of 16 years ago, where computers took 5 minutes to boot Windows, where device drivers and such were a mess, and things were constantly entering and leaving systems.