Hi Manuel,
At this moment, the GPD for jBPM 4 is quite simple, and there are many features cannot be used on it, e.g. the properties of activity had not been supported completely, and there are still some issues didn't be fixed yet, e.g. if you enter the name of activity in property panel, the text will be turn to reverse. And some issues are depended by the PVM implementation, e.g. PVM had not supported variable declaration, so we could define process varaibles in GPD yet. So if you want to use GPD to design process definition on jBPM 4 there are still something having to edit source xml by hand.
You can see the roadmap from JIRA. https://jira.jboss.org/jira/browse/JBPM Because there are many issues that have not been fixed, so I said jBPM 4 doesnot complete.
At this moment, we are using jBPM 4.3. And of course we make some extension on jBPM 4 for our requirements.