I don't think it will ever happen "all together". For hard sciences you still need expensive labs and hands-on training. For medical schools, I'd prefer that an operating surgeon had some practical experience as well.
But a good portion of the courses (that frequently happen to be taught by TAs, not professors, anyways) belong online. One finicky part at the moment is testing, which relies on honor code, so there might be a move towards professional-level testing, the type you see for major exams (GRE, TOEFL) as well as professional certifications. Since most of the testing facilities charge money, it will probably provide a good reason for universities to charge for credits as well - you can still view the course for free, but to pass a series of tests and get credit you would have to pay.
But a good portion of the courses (that frequently happen to be taught by TAs, not professors, anyways) belong online. One finicky part at the moment is testing, which relies on honor code, so there might be a move towards professional-level testing, the type you see for major exams (GRE, TOEFL) as well as professional certifications. Since most of the testing facilities charge money, it will probably provide a good reason for universities to charge for credits as well - you can still view the course for free, but to pass a series of tests and get credit you would have to pay.