MOOCs are still relatively new and evolving. After all, Rome was not built in a day. There are challenges ahead: revenue models, creadentialing, accreditation, course completion rate, student authentication, etc. As research in this area is developing, more data will emerge that would help to address the challenges.
As Thomas Edison said, "I have not failed. I've just found 10,000 ways that won't work". I believe him!