Your idea is not bad, however it is fairly annoying to teach more than 1 student at a time. I've been a sensei, twice even and believe me, having to explain a technique to several students at once and applying a certain teaching method.
As much as most people want training, and as much as it is undetstandable, being a sensei/senpai does not compensate you with anything, so I think the current training system is fine, as long as you can cling to the available senseis for long enough.
I may be wrong, do feel free to correct me, current senseis. Those are my two cents.
Edit: Also yhe synchronization would be terrible due to the different timezones.