Systems for selective dissemination of information (SDI) are used to efficiently filter, transform, and route incoming XML documents according to pre-registered XPath profiles to subscribers. Recent work focuses on the efficient implementation of the SDI core/filtering engine. Surprisingly, all systems are based on the best effort principle: The resulting XML document is delivered to the consumer as soon as the filtering engine has successfully finished. In this paper, we argue that a more specific Quality-of-Service consideration has to be applied to this scenario. We give a comprehensive motivation of quality of service in SDI-systems, discuss the two most critical factors of XML document size and shape and XPath structure and length, and finally outline our current prototype of a Quality-of-Service-based SDI-system implementation based on a real-time operating system and an extention of the XML toolkit.