In this paper we discuss challenges in collaborative mixed reality visualization. Despite recent advances in immersive technologies in general and, specifically, Immersive Analytics, systems rarely leave prototype status and are seldom found in real-world usage. Based on our ongoing research in Mixed Reality data visualization and experiences with our own toolkit for collaborative immersive visualization, CollARVis , we identify important challenges of such systems and examine possible approaches to address them. By doing so, we contribute to the ongoing discussion how future immersive applications can be made more practical for productive environments.