I tried to compile xfce4-panel 4.8.3 with libwnck 3.0.0, but it failed: - the configure not recognizes the libwnck 3.0.0, - after patching configure and configure.ac, the build failed: pager.c: In function 'pager_plugin_screen_layout_changed': pager.c:293: error: too many arguments to function 'wnck_pager_new'
libwnck3 is gtk3 and xfce4-panel is gtk2, you can't mix those.