I don’t know whether I’ll have anything to contribute to your research project, but I will be lurking 🙂 and let you know if I have any ideas.
As far as getting more people involved, there’s at least one very simple answer. Disguise your cMOOC as an interesting, preferably easy, xMOOC. Up front, you have a sequence of short videos and quizzes, for which you award a certificate of completion. Put all the cMOOC activities way off to the side, maybe even on a separate site, as strictly optional.
scottx5 is right. Most people are on a different wavelength. Some of them will never get the message. But many of them can. We just need to keep repeating it, one idea at a time.