At least in the past, at CDER Robert Temple would sit in a room with others, including DEA officials, and make the decision. Not exactly how it will happen now that Temple has a different role, focusing on clinical studies et al.
Still find it interesting that MRK stated that scheduling was not a big differentiator. They must have had some interaction with the agency on this. This brings up one additional view - that it will be Schedule 4 initially, then will come off the schedule after being on the market for a couple of years?