I'm pretty sure openrc uses (or has the option to use) cgroups for dealing with just this. Containerizing services isn't a new idea--Solaris and FreeBSD can do this already, for example.

Regardless of the init system, we've had the ability to control daemons with cgroups already for some time (cgexec and friends). Even in humble sysvinit, I can edit an initscript and ensure that the service it starts runs in a cgroup. Hypothetically, I could even do this inside of start-stop-daemon.