Strongly agree with all of michaelochurch's points, especially #1. Frankly, it baffles me that "career tracks" weren't (and still aren't) a core component of the MOOC product offering. (I actually applied to YC S13 with a solution to points 1-3.)

Duke researchers who actually taught a course on Coursera put together a comprehensive report on their experiences. In it, they specifically address the drop-out issue. I highly recommend it: http://dukespace.lib.duke.edu/dspace/bitstream/handle/10161/...