It is an incredibly contrived, fantastical scenario that is too grating to even consider.
Now, from a parable perspective, does the post mirror the principle of how wealth taxes work? Maybe, if you're willing to equate the entire market (or whatever communal entity we're using for the basis of assessment) to a weird little cult.
Not to mention, the calculation for wealth would probably be based on something less temporary than a fleeting moment in the markets.
Finally, the government would not directly take shares, so they would always be owned by you. Presumably with the stock price so much reduced you can simply purchase more at a pittance.
They wouldn't take shares, but I would be forced to sell shares in order to pay the tax bill, because I don't actually have that money just laying around. So I had 10M shares @ $1/share, share prices go up to $100/share. I get hit with a $900M tax bill and sell 9M shares in order to pay it. Price goes back down to $1/share, leaving me with 1M shares. How exactly should I purchase more at a pittance? I spent all the money I didn't even have paying the tax bill, there's nothing left in my bank account to buy any shares.
That sounds like horrible financial advice.
By this same standard, maybe Amazon is doing an immense service to humanity, and that is why so many people use the site daily, and actually enjoy doing so. So maybe Bezos should get to keep his billions as well.
Currently, gold retails at $1808 an ounce. So it would take over 15.6 metric tons of gold to be even worth a billion dollars. That is substantially more than an "old pile", and probably of historical worth, like contained in a ruined temple or wartime vault or something
The San Jose galleon as I mentioned is estimated to have about $17B of gold on it. I don't think very much is going to change about the world when it is raised.