Systems-of-Information Systems (SoIS) are a class of systems-of-systems (SoS) in which constituents are information systems and exhibit a strong business-oriented nature. Existing notations and approaches for specifying missions in SoIS have not been able to cope with particular characteristics of this class of systems, including the sequence and interdependence among activities, roles definition, and the dynamics of constituents to freely join or leave a SoIS. In this context, we claim that Business Processes Modeling (BPM) techniques and models could complement such approaches, offering support for requirements specification and an additional viewpoint for architectural specification of SoIS. This position paper outlines a discussion on the potential of BPM to complement mission specification modeling notations and presents some research directions and challenges for modeling missions in SoIS.