- I think churn on Readlang has the potential to be lower than more traditional courses, since it's impossible to exhaust the supply of novels and other reading materials, and reading is a habit that lasts a lifetime. Granted, you may not need the help of Readlang beyond a certain level, but I think that level is extremely high, and could take years or decades to reach.
- I have a fairly strong personal bias in favor of self study over teacher directed study. There are great teachers and I don't mean to diminish the work they do, but I believe that to learn effectively requires self motivation. (Good quote from Gibbon that Feynman uses in his Lectures on Physics: "But the power of instruction is seldom of much efficacy, except in those happy dispositions where it is almost superfluous.")
- Selling to students forces me to make the product better for reading and studying, which should be the primary goal. Selling to teachers will put an emphasis on features like the teacher admin panel that aren't directly useful to the student. (Analogous to Enterprise software, which sucks because it sells based on features useful to the administrators and not the employees that end up using it)
- If it's sufficiently good for independent learning, teachers will want to share it with their students anyway, in fact they already are, so they are still a useful marketing channel.
I'm not ruling it out in the long term, but for now, I'm sticking with individuals.