BTW, I really think this doesn't need to be RC. (Or, at least, should be stretch-ignore, because removing all the reverse-dependencies would be worse than just shipping with runit-init.)
I agree it's bad to leave a user with a broken system. But in this case, the user gets an appropriate warning: root@sid:~# apt install runit-init Reading package lists... Done Building dependency tree Reading state information... Done The following additional packages will be installed: cgmanager fgetty getty-run libcgmanager0 libnih-dbus1 libnih1 systemd-shim Suggested packages: pm-utils The following packages will be REMOVED: init systemd-sysv The following NEW packages will be installed: cgmanager fgetty getty-run libcgmanager0 libnih-dbus1 libnih1 runit-init systemd-shim WARNING: The following essential packages will be removed. This should NOT be done unless you know exactly what you are doing! init systemd-sysv (due to init) 0 upgraded, 8 newly installed, 2 to remove and 0 not upgraded. Need to get 439 kB of archives. After this operation, 1,059 kB of additional disk space will be used. You are about to do something potentially harmful. To continue type in the phrase 'Yes, do as I say!' ?] If I get such a warning, and answer explicitly by typing "Yes, do as I say!", I'm not surprised if the system is broken afterwards. And in this case, the brokenness is easily fixed by hard-rebooting, if I understand it correctly. Not nice, but not a catastrope. Jan