Currently we have a "Customers who have bought x but not Y" report for products, allowing them to quickly and dynamically check which customers have bought certain products but not others.
There is no standard report for this that makes use of Magic matrix categories, you can use the build awareness feature to do this, but it does require making a campaign and doesn't offer any other ability to filter down results as a report would.
Adding this would improve our customers ability to report on Magic Matrix data and target their customers for marketing based on the results.
