Per-Graph local blackboards is a high priority work in progress feature and when it’s done it will work pretty much the way you describe here.
Unfortunately though, until this feature is done, there is no way to have a per-graph blackboard and all nested graphs will share the same “root” object-based blackboard, or of course any of the global blackboards.
I am really looking forward for this feature to be completed and be part of NodeCanvas.
Gavalakis
