If you ask me, TA should be the more glorious position. There's just no point in speaking the same thing in front of 200 students every (half) year in front of 200 people with little to no interactivity. So what's the point of having that person in front of the class and not some recording?
Oh, right, there isn't one. There hasn't been for some years now, but the academia has had neither internal nor external incentives to innovate. Some might say giving the students the best possible experience should be an intrinsic motivation for professors. A shame it doesn't work that way.
I think though that TAs in Coursera/Udacity are not active enough. Given that tens of thousands (hundreds?) take a course, they can't afford to be. It makes me think that this model is not sustainable either.
I mean, in our day and age, dabbling in an area of science/art should not be a hard or expensive thing to do. And if you're willing to find your own information, it mostly isn't. But if everyone wanted to dabble in computer science and learn some basics, there just aren't enough TAs in the world to provide assistance.
There certainly would be enough learners, though! And I think that's a much more sustainable model. Udacity and Coursera both have active forums, I've heard Salman Khan mention it, and even in that "Intoduction to AI class" that did not have discussion forums from the start, people organized study groups, forums and subreddits all on their own.
Let's make it "cool" to study together and help others. Social routines will do the rest.