Systemd is on the wrong layer here. You need something that can set your machine up, like docker.

Systemd seems to be moving in that direction, the features are coming together to actually enable this.

Though imagining the unholy existence of an init system who's only job is to spin up containers, that can contain other inits, OS images, or whatever ..... turtles all the way down.

Okay it sets the machine up, but not the underlying host machine though.