We already do. I think most people in this discussion aren't realizing that the current sysV init system is an extremely small pid 1 /sbin/init, and most of the logic in external rc scripts. Moving rc scripts to systemd declarative syntax is fine.

The important part with respect to software architecture is less complexity in pid 1. Subprocesses of init can be safely updated and restarted. More code in init is a real problem -- that's why systemd as pid 1 is controversial.