By “well prepared,” I mean someone who has had the necessary prerequisite learning experiences and who has succeeded in those experiences. A person who is well prepared is ready for the current learning experience in terms of prerequisite knowledge and skills.
This may be true in formal educational settings (to a degree), but I think it doesn't apply as much to MOOCs. Depending on the content of the course, an open, online course provides all participants to share ideas in the manner they choose. Learning can occur not only through question and answer, but simply through a process of sharing diverse opinions. Sharing diverse opinions can occur regardless if one is a novice or expert as terms such as "novice" and "expert" can be misleading representations, even in formal circles. That's why ZPD falls short in adequately explaining how people learn in real life; that is, that we learn when we teach others regardless of the expert or novice labels. When there is open interaction, invariably individuals are teaching and learning through an iterative and reciprocal process. Teaching others can occur at many levels and this is what ultimately happens in a MOOC - Instruction occurs most often through the participants themselves.
Depending on the subject matter, it is quite possible to enter a MOOC unprepared and leave prepared (the act of becoming prepared is a learning process). The point really is whether a person knows more after (and because of) having taken the MOOC or not?