Once we have the ability for plugins migrate the OSGI, the next step is to move the "core" code into OSGI as well. This involves moving the OSGI container from an isolated embedded space to become the top-level container of the system. This migration is easier than it sounds. The "core" code left after 5.2 is all contained in the "pentaho" WAR. OSGI supports the deployment of WARs as OSGI bundles. The entire pentaho WAR will become one large WAB (Web Application Bundle). From there the work of separating out parts to their own distinct bundles can begin.
Also in 6.0 is the switch to the OSGI Service Registry away from PentahoSystem. All IPentahoObjectFactories in the 6.0 timeframe will be updated to register with the OSGI ServiceRegistry. Once done the PentahoSystem.getXXX() calls can be migrated away from our code to simply call into OSGI. Once this is done we can start the process of deprecating the Pentaho-Specific APIs and transition to plain OSGI.