1) The most powerful weapon in the world is the mind, but you must be taught how to use it, and this is just what reading and language arts may do. 10th, 11th, and even 12th grade reading and language arts will make for incredible additions to Khan Academy, and will definitely be greatly appreciated by those who hunger for more, and also those who don't quite excel at it. 

2) Slightly related by intellect, I should be inclined to bring up critical thinking. Such a course would fit in life skills, but it will be a great addition anyhow and serve similarly to reading and language arts.