I have often marvelled at the wastefulness and inefficiencies of the current teaching system. If you have an exceptionally good teacher they should be teaching millions, not a year-group of 100. If online learning took off I think it has the potential to dramatically improve education for people everywhere in the world, for a fraction of the current costs.
Having said that, there are numerous issues which would have to be sorted out. Academic education is (I believe) extremely scalable. Children's emotional, social and physical education is less so. The results of such an education are extremely dependent on the child's attitude and willingness to learn.
At the very least, online learning has the power to completely change adult learning in the near future, where we can assume the above issues do not apply.
Some variation of this happens in HK, where everybody wants to learn English (because they can't learn as well from their peers, unlike other subject) and English lecture/tutoring places pops up all over the place, and the top teachers teaches, via video conferencing, hundreds of pupils at once. I'm told the top teachers gets paid in the millions.