A mailing list-based class might end up being similar to a writing seminar, in which individuals have time to make up their questions and responses. There is nothing on the net that requires students to search out a teacher in order to learn. These will be times when each student is on the infobahn, in the same net place, at the same net time. This will work pretty much just like the Valhalla MOO and the Aerosmith Tour. Office hours' can be dealt with via electronic mail, and many professors in 'real' colleges do this already.
Teachers can set up electronic displays that the students can visit.
They may not even have to type. Your child's video game is already teaching your child how to use electric gloves to control computers. The question of testing becomes important. But I think that the virtual school will become so necessary that the question of integrity will be resolved even if it means simply trusting the student not to cheat. That's really the way things are done today as well, at least in college.