Arch Linux will now support Systemd as the boot framework on on all its new installations. The news was announced in official Arch Linux site by Thomas Bächler. The systemd-sysvcompat package has been added to the base group and users will be able to use Systemd by installing this package.Some package may still require native systemd units, for which users have to install initscripts and add them as daemons.
Existing users will not be effected by this update. However its high time user switch to Systemd as future packages and updates may rely on it.
You can read the wiki instructions regarding installing Systemd in Arch.