How do you manage certification and credentialing?
How do you curb cheating and ghosting, having people do the work for you?
Will it create a raft of pointless low-worth degress in English and sociology and other non-lab courses? I.e., will it lead to a kind of Gresham's law applied to credentialing paper?
It's already been suggesting that flipping the classroom will lead to a revising of how to teach high school. They won't need many teachers. Have one teacher record the lectures or direct instruction and a corps of lesser-trained assistants to actually assist students. Perhaps have one master teacher per district, or outsource the master-teacher work to a consultant that will implement state-mandated content in a single lecture for a topic for the state.
Hard enough to keep kids from "playing school" in order to avoid learning--do the work in a pro forma fashion, getting good grades by making sure that all the blanks are filled in on paper but not worrying about the blanks being filled in in their brains.