Much of the magic of the Massive Online Open Course (MOOC) system comes from the professors robotic assistants: the software that keeps track of your course work and assignments and gives you instant feedback on quizzes and exams. What about essay questions? MOOC software can grade short answer questions, albeit a bit imperfectly, but I have no faith in its ability to deal with the longer form. For that reason, MOOCs have been experimenting with peer grading. I'm not sure how it's going, but I'm not optimistic.
Of course scholars and scientists are hardly strangers to peer review. It sort of works for science, but reviewers assigned are usually supposed to be experts in the field of the paper, and in any case have all accomplished earning some of the checkmarks of academic success - something hardly likely to be the case in your freshman composition course.
I suppose I will have to take one of those peer graded courses, but I'm not looking forward to either the giving or receiving end of peer reviews. Of course I don't much like reviewing others scientific papers either. It's hard and usually thankless work.