Currently it is my understanding that a node accepts data when fired. When an audio node is fired it currently can input and output an audio buffer. However when midi data enters the node it has to wait until the next node execution to enter the node. It is my understanding that other softwares employ a midi buffer to allow the node to access this data between fires- so as to allow audio midi realtime performance. (Midi instruments)
Possibly vuo could implement this in a new and exciting way- many possibilities - one is to time stamp each event- (midi and otherwise) to allow nodes to access sub buffer timeing if needed. This extra piece of data could be added to events at the port-type level. This way if a node wants sample-accurate timing it would be possible.