The -r2 bump of xf86-input-synaptics added the installation of an xorg.conf.d file (good). It also bumped the version dependency of xorg-server from 1.6 to 1.8 (bad). Since files in /etc/X11/xorg.conf.d are completely ignored by older servers, installing this file is harmless and the dependency did not need to be bumped. Therefore, the only thing this dependency does is make the downgrade path arbitrarily harder for no good reason: the driver works perfectly fine with older servers.
Both (synaptics 1.2 and xorg 1.8) no longer exist is the tree. Please close this bug.
marking as OBSOLETE.