Not sure where you hang, I don't have a Kinect or that kind of stuff but if you already have your skeleton and you want to create 4 different lines connected to the borders what about something as the composition below ? Perhaps it would need some Allow changes or some Hold Nodes but try that.
I'm not sure what you mean with "regular" beside black hole Jaymie but from the question Push rendering optimisation I still could think something like "allow data to passthrough without modifying it" could be cool.
Perhaps the available options could be hardcoded in the nodes because for all nodes that have 1 single input / output that would still be cool. And as Jvolker stated "what state would those nodes be in when I restart the application" I assume compositions could save the state just like other ports, exported apps would need some kind of preferences plist or something ?
Why would the 3 states not be possible generally, but some nodes only have 1 or 2 of the 3 ?
But if a node had a bypass like "continue to flow the data without modifying it", would the node still have to process or will it not process and therefore spare hardware usage ?