I think this hasn't been done well because it is more difficult than creating something like wikipedia. One of the reasons wpedia works is because you can enforce a non-redundancy policy. There can only be one article on any one topic. In education, however, there are many ways to teach any one concept. So you have to allow people to create different lessons on the same topic, but also create a simple pathway through all these lessons. Khan academy has been successful in this for math, but I think a good part of that is because there is one person clearly running the show, an intensely productive man who spits out several videos a day, for years. Crowdsourcing that work is an interesting challenge.

As a teacher, I'd love to see this done well. But it seems most people who go into these ventures either don't get education, or don't get technology. It seems there is a pretty small group of people in the world who really get both fields. It's also hard to put together a team of people who get both. And finally, the profit motive kills a lot of education endeavors. Education is fundamentally a human right, and profit motives tend to exaggerate the achievement gap. There is plenty of room for new thinking in this area.