This is actually the basic idea of an amazingly interesting book I read recently, _Good Video Games and Good Learning_ (http://www.amazon.com/Video-Learning-Literacies-Digital-Epis... and see also http://www.amazon.com/Video-Games-Learning-Literacy-Second/d...)
Lecturing would be left to professional speakers backed by a writing team and subject-matter experts, filmed remotely and either sold to schools as materials on the free market, or produced for the public by government media arms such as the BBC. If anyone had a question about the material that couldn't be answered by the lecture, the books, the rest of the class, by the "teacher"'s Socratic deduction, etc., the school would have tutors on-call as well (by remote from a tutoring group, or locally as a service of alumni.) There would be no segregated "classes" or "classrooms", but rather an integrated environment more akin to a combination library/study-hall, with gatherings for people working on the same class of problem at the same time, etc.
In fact, there wouldn't really be a need to "graduate" at all, or to "register" for specific semesters. As long as you could get a print-out at any time proving you had 100%-ed the problems relevant to the job you're applying for, that would be all you would need. You would be able to show up one day, leave for years, then come back and resume your studies as if you had never left. In fact, done this way, people would probably stop considering themselves to be "in school", but rather just say that they "go learning" in the same way one would "go hiking" or "go to yoga." A life-long hobby, in other words—just the way an education should be :)
Ah... but if only.
Right now, teachers act like role models for kids, but they're an intrinsically bad fit: kids want to see their role models doing the things they want to do, but teachers simply teach. Ideally, role models would be "visiting fellows", perhaps alumni, of a completionist school, psyching kids up about doing some thing or other such that they see school as a step toward doing that thing. Without that, school is meaningless, and it's no wonder kids aren't interested in it.
A lot of people feel the same way too about PhDs teaching, but universities are so huge they're like governments unto themselves full of traditions and factions and general bickering. I could really see value in the system you propose.