One of the ideas behind dbus (and one of the ideas behind systemd! They're sorta linked in this way) is that services should be able to activate on request, like httpd but for local IPC. You could make a stand-alone dbus, but you'd have to either give up on socket activation, or re-implement half of the systemd service manager to make the dbus server responsible for spawning socket activated daemons.

Both of those are totally possible and would probably be interesting for non-Linux systems.