Salman Khan is better than 99% of teachers. We really don't need nearly as many of them as are employed.
On the other hand there is this line of thinking that sounds plausible, that we have the idea of instruction and homework backward in our school system. Kids should watch videos by great instructors as homework, and should do the exercises (what would normally be the homework) in the classroom. With the role of the teacher in this scenario to assist students where they have difficulty. This way the teachers aren’t spending 80% of their time doing the repetitive stuff that’s the same for every student but can instead focus more time on the problem areas students are having.
And how do you ensure that it isn't really just a proxy for being poor? Since hunger, lack of a long-term home, parents who need to work multiple jobs to support a family, etc. are things which make it difficult even for smart and motivated students to learn.
Of course there are some smart and motivated students who can learn from books and online resources. But is that all of the remaining 60%? Or is it 5%
Bear in mind that Khan Academy disagrees with your assessment that it can be a general purpose replacement for teaching. Quoting https://en.wikipedia.org/wiki/Khan_Academy#Criticism : "Khan Academy positions itself as a supplement to in-class learning, with the ability to improve the effectiveness of teachers by freeing them from traditional lectures and giving them more time to tend to individual students' needs", so KhanAcademy" (emphasis mine).
I would consider my experience with education sub-par at best, but even I know that this will NEVER be the case.
http://www.oecd.org/pisa/test/PISA%202012%20items%20for%20re...
It is depressing to see how much the quality of US public education has declined while the spending has increased.
But it doesn't have to be this way. And that's what makes it so sad. One look at an 8th grade primer (math, language arts, geography, history, any will do) from the late 19th Century or early 20th Century and it is clear American public education took a very wrong turn somewhere along the line.