Suggestion: if the instructor can also bring in another knowledgeable person, they can receive real-time email/chat questions, and try to answer them, or aggregate them in a meaningful way so that the instructor can address them.
I don't know how well this suggestion will work in the general case because it requires two people who are capable of teaching the course, but it may help. Particularly if the person fielding real-time questions starts seeing trends.
Also, if you can't do that, maybe you could set up chats with 6 (or so) students each, who could try to answer each other's questions.
In theory, you could do it with one, if you were prepared to make a leap in the delivery.
Breaking up a 200 person class into 20 person groups would entail repeating the same material 20 times. Instead, it could be done live once, then replayed to those groups. The tutor could then devote all of the text chat time to Q&A on each live session.
That's an interesting concept. It would be helpful to see that other people are having the same issues in a given class. I wonder how successful an automated system would be based on key words. Something like a twitter stream for a live feed, but more concentrated to focus on recurring questions.
I don't know how well this suggestion will work in the general case because it requires two people who are capable of teaching the course, but it may help. Particularly if the person fielding real-time questions starts seeing trends.
Also, if you can't do that, maybe you could set up chats with 6 (or so) students each, who could try to answer each other's questions.