How about additionally introducing an xfconf property (e.g. /general/show_position)? So downstream packagers can build Xfwm4 with this option enabled and still offer a runtime configuration for their users who don't like it and find it annoying. For example, see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1014212.
Just in general, having it as an easily accessible, changeable option makes more sense. What if the same user gets fed up with it? What if they wanted to try this option but didn't like it?
That would require just wrapping the relevant parts of the code with if (xfconf_channel_get_bool (channel, "/general/show_position", FALSE)) statements, right?