Unfortunately, I must delay the 0.4 release because I have other priorities for now. The tentative release date is by the end of August.
The SVN head, available at https://py4j.svn.sourceforge.net/svnroot/py4j/trunk, contains the most important new features and bug fixes of 0.4 so do not hesitate to use the code from the repository. In fact, I use this code every day for the tool I’m developing for my Ph.D.
As always, comments are welcome!