Which init system for Debian?

There was no shell hairball of init scripts needed with the super-daemon approach. The super-daemon could be launched and *managed* directly by init (inittab), and the super-daemon monitored things (sockets, ttys, etc) and launched services on demand (which could well go on to handle multiple requests, see, e.g., the wait option in inetd/xinetd).

The shell SysV init scripts were indeed a hairball and problematic and racy wrt start. I'm not saying anything to the contrary on that.

All I'm saying is that daemons to monitor resources, launch service handling child processes on demand, and manage their lifetimes (respawning, etc), have a long tradition already in Unix. I'm still curious what it is that can be done in PID 1 wrt child management that is impossible in the more distributed fashion? (And be careful not to conflate what was added to the process management capabilities by cgroups, and used to good effect by systemd, with functionality that is uniquely implementable in PID 1).

(Ob monolithic - Systemd apparently is modular only at compile time, not quite the modular/monolithic distinction I had in mind in my earlier comment).