How will they deal with it if they received $150 million dollars in ETH today, but a few months from now that's $5 million and they owe taxes?
If I were to get $150M today, I would immediately start selling what I expected to owe for taxes. Then I could hold the rest after the crash.
If you don't have such foresight, you WILL be forced to sell it all. Also, while (estimated) taxes are due on a quarterly basis, the reality is that you'll have until April 15th of the following year (i.e. longer than the 3 month power down) to power down and sell. (The 2-year power down could have caused a nightmare scenario though)