the textbook/education industry is probably the largest on the "change the world" scale. It would take a really adventurous and patient VC and/or Angel group. You would also have to have a good group of advisors and/or team members that knew the space. It's a long long term company, but at the end of the day it would probably have the largest impact. If I were a VC, I would fund the right team to do this without hesitation.