Cascading parameters feature was implemented in the old reporting tool (JD) as an add-on distributed per customer request. It was implemented on the client side (DHTML+JavaScript), which required pre-loading all the data to populate input controls. So for example of countries and cities we had to send all countries and cities to the client and then apply JavaScript to show only cities for selected countries. Sometimes this approach presented performance problems. For JasperServer implementation I suggest using Ajax for dinamically retrieving list of cities for selected country. So far multiple customers requested this functionality, but none came as far as sponsoring the implementation of the feature. Perhaps once we implement this, we can offer it on eShop?