You're out of your mind on this one.
Let's say my Bitcoin takes me over $5M in net worth... but I never sell it. You're saying I've to come up with over a $m in cash to hand over to the IRS. So I'm forced to sell just to get some cash. Then what if it crashes, as it tends to do? I just paid a bunch of money for gains I do not have
Or, what it goes back up to $5M again... I have another multi million tax bill. But the more likely scenario is the asset crashes because everyone would have to sell a huge chunk just to pay the damn bill.
What if my house appreciates? What if all my cash is in my house? Do I have to sell my house to pay the tax bill? How is that good for me? Or the country?
You would have a tax basis and the government would need to give you a massive credit for periods where their are unrealized losses that are in excess of your original cost basis.
But you'd still be in a good position because you're holding a valuable asset.