The chance to make a meaningful impact in people's lives.

Sal Khan and Sebastian Thrun both commented on the letters I support they received. Many people were deeply appreciative - and they were often outside of the typical university demographic. Single mothers, the unemployed, people switching careers, third world students, those who never got the material using traditional methods all told them how their efforts changed their lives.

These teachers are already materially successful. Their work was intellectually stimulating. But this type of feedback was something new for them. They could help thousands of people. It's very hard to ignore that possibility, and go back to your day job.

I have no doubt that Agarwal has already had similar feedback from MITx. He likely had no choice but to fully commit to it.

PG recently commented that moving YC to silicon valley was both the ambitious choice and the self indulgent choice. That's an irresistible combination, and these professors are in the same situation. They can be push their field forward with the knowledge that their are deeply impacting the lives of thousands of fellow human beings.

I think this is a very big thing.

I'm taking two free Stanford/Coursera classes (PGM and NLP) and in return for a lot of my time (about 15 hours per week, per class), I have the opportunity to master two topics that interest me.

These "superstar academics" themselves have the opportunity to positively affect the lives of a very large number of people.

The potential they have to massively disrupt the way higher education has been done for hundreds of years..?

You might rightly ask for evidence to back that sentiment up; I guess its hard to validate that something has disruptive potential, ahead of time. But isn't hundreds of thousands of students signing up, evidence of something?

Before universities, guilds would have members vouch for their apprentices. If you were a master blacksmith, your word saying that your apprentice was skilled enough to be called a blacksmith was enough for them to go out on their own.

It's not the same thing but its swinging back towards that.

Imagine getting in on the ground floor when they started the first universities in western history -- Oxford, Cambridge, the Sorbonne, Heidelburg, La Sapienza, Jagiellonian, Salamanca... we could be those guys!