Real money gambling is legal in many non-US countries. It's also legal in many individual US states.

https://en.wikipedia.org/wiki/Gambling_in_the_United_States#Legality

The problem is that if they make real money betting available to even just one person somewhere in the world, everyone else can sell their mana to that person and it becomes effectivly real-money everywhere.

Maybe that'd be ok as a legal fiction, but probably not. (If it were possible I'd expect e.g. Polymarket to have done it.) But what if they banned the sale of mana from people in areas where it can't be cashed out to people in areas where it can? Or created a separate currency that can influence the probability of the same markets? There might be some way to make it work.

Market resolves subjectivly once I'm reasonably convinced of the answer. I'm making this as a discussion post and a way to gauge a general "vibe" of whether it's doable, rather than as a rigerous prediction. I won't bet.