I think X should force installation of acpid to offer ACPI fully. In /var/log/Xorg.0.log one can see in such a case when acpid is running: (II) Open ACPI successful (/var/run/acpid.socket) otherwise the deamon cannot be contacted.
xorg-server works just fine without any acpid daemon. Furthermore, it's only a run-time dependency. Forcing it is useless. It's up to you to decide if you want/need acpid or not. Thanks