The current version in ports is 3.36 whereas there is now a 40.0 version. From a quick look at the changelog, there doesn't seem to be a change in dependencies.
Should we create x11-toolkits/libwnck4 instated to keep x11-toolkits/libwnck3 for ports that want to keep 3.*.
(In reply to Eric Turgeon from comment #1) Why? It is always the 3.0 API. GNOME developers have chosen different numbering. It follows the GNOME releases, see NEWS file in their repository.