Hierarchical structure for all links is going to happen, so really this could be easily expanded to include lists or even all blocks.
It would be really cool to be able to see trees in the graph view, especially when we get to the point where the contents of the graph view can be granularly controlled and saved. I can imagine having two (or a higher number of) trees whose blocks both link into a third collection of objects, and being able to use the graph view to quickly see which in the third collection are linked to by which one or both of the trees.