Architectural decision modeling aims at supporting the software architecture design process by capturing a reusable body of architectural knowledge. Whereas significant progress has been made towards this vision, there still remains a number of open problems. This paper outlines selected research challenges and opportunities related to knowledge capturing and sharing, model evolution and verification, and the integration of the architectural design process with existing software development methodologies. Our goal is to start a discussion on a roadmap for future research on reusable modeling of architectural decisions.