All >=consolekit-1 versions have a
dependency. But glib[dbus] just pulls in dconf, and nothing else anymore. If you really need dconf, please depend on it directly, but I doubt you do. If it was added for something else, you might have a problem by now, as that's all glib[dbus] does nowadays (and I'm trying to get rid of it).
If you need gdbus-codegen during build, then you want to depend on that at build time directly (it's split out by now). If you need GDBus API, then that's always built by dev-libs/glib, USE=dbus doesn't matter.
Please get rid of the dbus USE dep in all consolekit ebuilds after review.