I do think you need to have deadlines. They can be more flexible but deadlines help at least keep groups of the class at the same pace. The more people participating, the more relaxed the deadlines can be. I've seen some courses that have so many people, you could honestly take the class at your own time & always have people to discuss the current lecture with.
In the case of a real MIT online degree, I would support a schedule that mimics the campus schedule. If you have other schedules/travel/etc., then sign up only for 1 course at a time & understand what you're committing to.
I get scaling is hard the more "real" you make the course. I feel you can have a nice balance between hiring assistants to help with grading & discussions by increasing the cost somewhere in between on-campus & average MOOC prices.