Coursera and other MOOCs are media properties that monetize viewership (thorugh certificates rather than ads). As media properties, michaelochurch and others are right that the synchronous model isn't really going to work in the long term.
I think ed tech should be about connecting teachers with the content they need to teach (and I'd include self-educators amongst 'teachers' here). Students need synchronous access to teachers, but those teachers don't necessarily have to have created that content just now. This suggests that online education might look more like a 1:100 teacher-student ratio rather than 1:100k. Nothing's more motivating and engaging than a human being.
Personally, my best experiences have come from two sources: self-study from great materials and guided study from great teachers. This suggests that a role for ed tech might be connecting great teacher with great content rather than broadcasting teacher-as-content. Personalization, engagement, motivation, etc all come for free if we empower great teachers rather than seek to replace them.
It's misguided to think that some professor from a great school can best deliver the content to all audiences. Imagine great open content accessible to every teacher for use in their own classrooms. With an inverted model of teaching, the lets them push content out to the students for self-study and then have synchronous classes where they, the teacher, can motivate and customize the delivery of tough concepts for their particular group of students.