As far as I understand, you need to be root (or another privileged user) who has write access to /etc/init. Conclusion: You can bring down a machine with superuser privileges. Breaking.
1. Apparently it watches all of /etc, not just /etc/init,
2. Which means that writing large-enough config changes in some part of /etc you thought was completely unrelated to init can unexpectedly take down your box.
That's not good, and not something that can be dismissed as "of course superusers can turn the box off".
What really caught my eye is that this affected a newer init system, specifically because it was more dynamic (using inotify), which has been a goal of many init replacements. I'm curious if this affects other init systems, specifically old init or systemd. Or if you could find similar attacks against other init systems.