Likewise, this is now important to us.

As new Zendesk customers, we were actively developing a solution whilst using the product. Therefore older tickets do not contain all of the information we require for effective reporting.

We are now looking to report on historic workflow, and are unable to do this because closed tickets are frozen with insufficient data within them.

As a workaround, I attempted to create a custom report using Gooddata, but this utility is not powerful enough (I cannot filter subjects 'like' a certain keyword, or search ticket activity for keywords).

We're therefore completely stuck, and Zendesk currently offers no solution to what must be a very common requirement among users.