Good idea in theory. But, as Yogi Berra said, in theory there's no difference between theory and practice. But in practice there is. Here's how to get around the political and financial barriers to getting liquid tax revenue out of hard to value illiquid assets: index a wealth tax to the Gini coefficient measure of inequality. Inequality drops, the top 1% get a tax cut. Inequality rises and the wealth tax rises. https://medium.com/the-national-discussion/how-to-stop-the-plutocracy-game-index-the-top-1-s-tax-rates-to-decreasing-inequality-a3a19f42cd97