I don't know. I suspect the true answer is "there is no fair way to tax people equally across multiple orders of magnitude of resource ownership and multiple wildly different types of resource," especially when dealing with individuals who are approaching the same economic ballpark as the governments that are attempting to tax them. I'm just pointing out that capital gains being taxed "eventually" isn't watertight.
And it's not as if the current system is fair. You regularly see cases like that kid who won a trip to the ISS and had to give it up because it was valued at $X million dollars and to accept it he'd have to somehow pay hundreds of thousands of dollars in taxes. There's also the issues with stock options that come up here from time to time, where someone is owed millions in options that they can't actually use because they'd have to first pay a percentage of the value in taxes.
As someone who is currently undergoing a tax audit for a year in which I reported ~$20M in cryptocurrency trades but only realized about $10k in income from them, I can confirm that "fairness" does not appear to be a goal of the tax code. Cryptocurrency (and especially derivatives) really exposes some of the head-scratching aspects of the tax code around capital gains.
And it's not as if the current system is fair. You regularly see cases like that kid who won a trip to the ISS and had to give it up because it was valued at $X million dollars and to accept it he'd have to somehow pay hundreds of thousands of dollars in taxes. There's also the issues with stock options that come up here from time to time, where someone is owed millions in options that they can't actually use because they'd have to first pay a percentage of the value in taxes.