There will for sure be a regulator to stop that. In fact, there are already numerous regulators to stop it. If you want to hold deposits for your customers who happen to be California residents, then you are a bank and will need a banking license from the California Department of Business Oversight. California does not care what currency those deposits are denominated in. I expect this to be true everywhere else in the world, cryptocurrency is not some alternative universe where the old rules won't apply.
