You can check out my lectures here http://inperc.com/wiki/index.php?title=Category:Courses (math only). These are written lectures but they start at about the same place as Khan's (in a real classroom though). Hundreds of illustrations but I haven't figured out the "interactive" part yet.
Of course, make it interactive and with lots of visuals for better learning.
There you have it, a great idea for a startup.