Join us January 15th for an AMA with Champion Achaia Walton, who will be talking about her article on Event-Based Reporting and Measuring Content Groups!
This seems like a bit of a miss by Adobe if this doesn't exist - although maybe they were worried by how 'instance' would work across multiple values set in the same hit.
Could you work around this by using a processing rule to set an event whenever the list var is set?