Aiming at bridging the gap between the recent advancements in eXtended Reality (XR) research and real-world scenarios, in this paper we describe an iterative user-centered methodology developed to elicit user requirements and to design the scenarios for a multi-sensory collaborative XR platform. Τhe platform aims to be customizable and flexible, and is intended for use in different pedagogical contexts, instantiated by two pilot scenarios: a) XR training for first-responders and fire brigade staff at international airports and b) XR informal learning experiences addressed to visitors of museums and cultural centers. Through a series of workshops and focus groups with users from relevant organizations, we collected a total of nearly 100 pedagogical, technological, experiential, operational and other user needs from within these two different contexts, and discuss here the challenges and limitations but also the opportunities that were encountered.