Progress on the new metamodel ended up being much slower then anticipated, so we decided to move ahead with the 4.0 release and will continue development of it after 4.0. At that point the rest of the work for 4.0 had already been completed which brings us to the first CR release. The complete list of its changes can be found in the JIRA release notes.
Hibernate Core 4.0.0.Beta2 has just been released. Most of the work in this release deals with continuing to tidy up the new metamodel. The complete list of its changes can be found in the JIRA release notes