It would be incredibly useful and powerful to have some level of relational algebra available at the Reporter level. This would allow users to take two separate Reporter macros and join them to a single record in a report based on some matching expression. This is currently possible only in a limited way by embedding a lookup in individual reporting keychains.
One way to do this would be a new reporter called Joining Reporter. The body would contain two reporter macros and you'd have a few parameters:
The reporter would return a Joined object similar to the way the Expanding Reporter works so that you can reference the objects in each set.