Adam Williamson has a patch for changing live images to replace some usage of sysvinit with systemd in https://bugzilla.redhat.com/show_bug.cgi?id=739446 .
This is a significant change that people should be thinking about. We really should be moving in the direction of using less sysvinit and more systemd going forward.
At first glance I don't like the creation of supporting files for each spin, but it may end up being the best way to do this.
It would be nice if people interested in live images would critique the ideas in the patch and suggest improvements or alternatives for moving toward replacing sysvinit with systemd.