This is exactly how DD13's high school is structured. Eight classes, four a day on alternating days. Plus on certain days they squeeze in a study time for a) working on assignments b) getting help from teachers c) meeting with student groups to work on projects.

Now as for the subject matter expert issues, that's different. DD is planning on bringing home her Geometry text in order to, you know, actually learn some math... instead of having psudo-Social Studies time in every class.