So I spend 30 minutes to set up an LLC and then transfer my assets to that LLC. Now, I don't hold the assets; I hold a stake in a privately-held company.

Ultimately, the solution you come up with needs to be at least somewhat airtight; otherwise, it just penalizes people who spend less money on tax advisors. The generation of income is a fairly well-defined point where assets change hands and you can apply some quasi-clear rules. Ongoing taxes on the potential to make money are a lot harder. So I buy some gold bars or valuable paintings and stash them in the attic. Gold / Picasso appreciates. How do you tax me on that? Do I submit an inventory of everything I own to the government every year? How does the government check - do they get to rifle through my stuff every December?

And hey, here's a cool one: if my parent owns a company and puts it in their will that it's mine when they die, is that promise an asset I owe taxes on every year? It's clearly worth something: it's potential money down the line.

Let’s do the bog-standard obvious and sane thing and pick a single point in time, once a year and use the value then. Maybe, i don’t know, close of market on the last trading day of the year. At which point it won’t fluctuate again until the new tax year. Then, we can call it “mark to market” because we’re marking the value to the market at a point in time.

Finally, we stop with silly bad faith arguments because fluctuations in stock have been successful taxed for decades. This is how day-traders pay taxes, and it’s not even a little challenging to do.