Continuing on the OSGi side, i've added a new maven module named activiti-osgi-rest.
This module is an OSGi Web Archive, meaning it's both an OSGi bundle and a Web Application. Any compliant OSGi Web Application extender should be able to pick it up and launch it. The main differences wrt the activiti-webapp-rest module is the fact that most of the libraries have to be deployed as OSGi bundles instead of being included in the web archive itself.
I'll try to add some integration tests for all the OSGi bits to make sure things are not broken in the future.