The monitoring functionality in GIO is modular: it is backed by different loadable plugins that implement OS-specific functionality. In particular, GIO uses an inotify module in Linux and a FAM module everywhere else.
Up until now, the devel/glib2 package in pkgsrc provided a build-time option to specify whether to build the GIO FAM plugin or not. Given that this plugin is built as a shared object that is loaded dynamically at run-time, having a build-time option for this is clearly wrong: it gives no choice to those relying on binary packages (e.g. end/new users). Furthermore, it adds a dependency on the ugly-FAM at the very bottom of the huge Gnome dependency chain. (As already stated, FAM is outdated and hard to set up.)
So, based on this, I've just removed all FAM support from devel/glib2 altogether and packaged its loadable module as sysutils/gio-fam.
Now waiting for a clean rebuild of the Gnome packages to see if the desktop now works on my machine by avoiding FAM/Gamin.