Maybe there should be 'gconf' useflag? In configure.ac gconf dis required only if --enable-migration=yes (which is default) But I think that most gnome-3 systems has already migrated to gsettings, so this dependency should be optional.
Well, migration was added at 3.7.0... I think it would be still too soon to drop/disable the migration as 3.8 was only stabilized recently (and only on amd64 and x86)
we dropped it in 3.14 cycle