I'm working on development of the appleseed plugin and I'm trying to wrap my head around using the new ability of the Pointer Property to be used with the custom properties we add with that exporter.
Specifically we use the node system with our materials. Right now a material references it's node tree via a bpy.props.StringProperty. While this works it has serious shortcomings for linking and appending. From what I understand we should now be able to have a pointer property in that node tree reference that connects the actual node_group datablock to that property. I'm still a bit green on Blender's Python API so I'm not sure how to set that up.