If I can pay property taxes on the unrealized value of my house, a notoriously illiquid asset with a notoriously subjective and noisy valuation, then billionaires can pay property taxes on their galactic piles of unrealized gains, which are more liquid than a firehose and easier to value than a $2 bill. This could crash the economy if done too aggressively, but the same can be said of every important economic decision ever made.

We've been pushing all the money into the capital economy and all the taxes into the labor economy and this can't go on forever.