I knew that my ebooks would go up against the Khan Academy. I just hadn't looked at the KA in a while. They've made many improvements in that time; exercises, more videos, and achievements. I spent about an hour there earlier this week and highly recommend the site.
I also realized that my ebooks wouldn't be a complimentary source of learning, it would be a direct competitor. For my $2.99 - $5.99 ebook, someone could get a 5-10 video (or even two or three) on the subject alongside a great number of exercises for free. Can't compete. I don't want to spend hours on this if I know it'll be a waste of time. It's too much of an opportunity cost; time I can spend elsewhere.
Overall it wasn't a bad idea. I just came across it years too late. The only way I could make it work is if my ebooks were also free. Once I had enough ebooks, I could work with the KA. Unfortunately, I have too many things I want to learn about and do. I don't want nor need to make money from everything I spend my time on, but a side income to let me be more choosy about my job would be nice.