Part of me wants to believe that that this would work and that there's some mix of rules and enforcement that would solve a diversion problem, but part of me also thinks that it could just devolve into a drug prohibition 2.0 cat and mouse game.

Probably a low barrier to entry for obtaining licensing would prevent a lot of diversion, basically excluding people considered too at risk (teens, mentally ill, etc). But there's always the risk of some meaningful number of people who are just non-cooperative with obtaining a license.

It's still an interesting idea.