I would say that license and all of that matters in the sphere of centralization. If you are a centralized casino owned by one person or one company then it means that you need to get a license for sure, that is how it works. However if you are decentralized, if there is no owner, it is just a software basically written to allow people to gamble against each other without any centralized authority, then why would we need a license?
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I don't think there is such a thing. Someone has to provide the platform so that players can find each other and compete against each other (a matchmaking system, so to speak). This would then also be the "owner" of the casino and would have to ensure a license, even if the games take place between the players of the platform.