I think you are missing the forest for the trees. Systemd is not just PID1, it is an umbrella project for various core system bits and pieces. Most stuff in systemd project do not run in systemd PID1.
Various core system bits that are tightly integrated using undocumented APIs and assumptions about what the other parts are doing internally which are subject to change at any time. I think you can replace some, though not all, of the non-PID-1 bits with a little development work, but replacing the core parts is unsupported.
That is beside the point. The argument was "That's not the init systems job." to which I presented the counterargument that systemd is not just an init system.
See my comment at https://news.ycombinator.com/item?id=7639730 - those are the external APIs used by software that isn't officially a part of systemd but still depends on it. The APIs between different parts of systemd are undocumented and subject to change. In fact http://www.freedesktop.org/wiki/Software/systemd/InterfacePo... says as much itself and exists in part to convince people this isn't a big deal because in theory someone could write their own components that implement the same APIs. (Except that in practice no-one has reimplemented anything beyond the most trivial APIs, and in fact that page claims some critical stuff like logind cannot be independently reimplemented or used without systemd.)
The systemd init is FAR more complex than a basic init.
Service status management? service file (of all types) parsing? IIRC all done in PID 1, with a nice (?) dbus integration and a glib loop added in for some additional fun.
Some think this is dangerous and not necessary.
