I would like to see a Customer Satisfaction (CSAT) functionality in Zammad
Right after that a ticket has been resolved/closed we could ask the customer his feeling about incident handling.
Something like 1 to 5 or 10 stars (★★★★★★★☆☆☆)
It could be also a good idea to give him the possibility to express himself with a small text field.
Also this mechanism could be extended to rate KB articles as well.