Transitional collaboration is a unique form of cross-reality collaboration within transitional interfaces. Despite being at different locations of the reality-virtuality continuum, users can closely collaborate and overcome traditional boundaries of space and time. Despite the renewed interest in transitional interfaces as a specific type of hybrid user interfaces, this form of collaboration remains relatively under-explored, primarily since suitable analytical tools and frameworks have been introduced only recently and traditional models from the CSCW community may not fully capture the true nature of transitional collaboration. Therefore, in this position paper, we present the current state of our work on formulating a new model that integrates classic CSCW models with more recent research findings from cross-reality and mixed-reality research on transitional interfaces. We present examples based on existing systems and theoretical literature to demonstrate its practical application, including the visualization of different types of transitional collaboration.