People can vote that a new tax should be levied on billionaires, but can't vote how those billionaires will react to the tax. Moving out of state is one option (see Larry Page, Sergey Brin, etc). Hiring armies of lawyers to challenge any wealth assessment is another. Litigating to the Supreme Court yet another. I'm not a billionaire and never will be, but if I can think of these few ideas, they can think of 100 times more.