1) OSGi allows us to deploy java modules independently. This lets us open source some of our code but not all of it. It is also provides a sandbox for contributors to work in. We don't want to discourage contributions to our project but we can't police every single change made.
OSGi has radically changed the way we design extensibility into our applications. We will need to meditate on how the dataflow components will register themselves and can be looked up dynamically at run time.
2) We can do a proof of concept using your standalone diagramming tool but would eventually have to embed the diagramming tool inside a larger application.
When we adopted OSGi we reluctantly abandoned Swing and started to build our application using the Eclipse Rich Client Platform. We can maybe use the Java2d portions of your implementation inside of an SWT application. However, that piece of the diagramming tool could also be reimplemented to use the Graphical Editing Framework (GEF).