But its not, for a reason, and there are existing reasons why companies don't tend to go public while still in the meteoric valuation growth phase.
And when companies are public, so that stock is a tradable asset subject to the tax, you can borrow against it; with sustained rapid appreciation, the interest rates will be substantially below the rate of appreciation, so there is no reason to liquidate assets to pay stock. Without sustained rapid appreciation, liquidating sufficient stock to pay the taxes won't force people to liquidate the bulk of their holdings, even over a long time.
But its not, for a reason, and there are existing reasons why companies don't tend to go public while still in the meteoric valuation growth phase.
And when companies are public, so that stock is a tradable asset subject to the tax, you can borrow against it; with sustained rapid appreciation, the interest rates will be substantially below the rate of appreciation, so there is no reason to liquidate assets to pay stock. Without sustained rapid appreciation, liquidating sufficient stock to pay the taxes won't force people to liquidate the bulk of their holdings, even over a long time.