well, my initial concern that this is turning into more like something like e.g. java, where you have to 'create a class' before you can do anything, rather than python, where you can just do what you want. I understand full well the power of grouping and reusability in the abstract, but! creating non-functional empty group nodes first is not the way to go, imo. make simple things easy, make hard things possible and all that.
that being said, I don't want to come off like I'm detracting from this. Looks like a potential leap for the particle system in blender... now I just wish all of blender was like this ;) (modifiers, constraints, object relations, transforms, etc.)