This paper presents our work-in-progress study on reference architectures as boundary objects for realizing trustworthy collaborative Cyber-Physical Systems (CPS). Furthermore, the preliminary results from interviews with systems engineering experts from industry and academia are also discussed. The interview results reveal challenges in using reference architectures during the system development process. Furthermore, exactly which trustworthiness attributes (security, availability, reliability, etc.) should be addressed to realize trustworthy collaborative CPS is identified as an open question, which we will address in our future work.