While recent advances in middleware and Software Engineering are at the edge of making Software Reuse a reality, the newly given dynamicity and openness seriously challenge validation , especially regarding Quality of Service (QoS). Modern QoS models require highly accurate quantitative descriptions of future execution environments, whereas these environments are getting more and more uncertain as dynamicity and openness increases. As a result, our ability to validate QoS concerns diminishes until a point where its worthiness must be reconsidered. In this context, we envision in this paper an alternative approach to reconcile dynamicity, openness and QoS. It combines run-time and design-time validation together with advanced modelling of uncertainty. We describe the overall process and discuss several obstacles to its realization, including QoS requirements modelling, QoS validation and run-time QoS fault-detection.