As the link in the post says, there is an exit tax in place to prevent just this. One of the qualifying prongs to be subject to the tax is "Individuals with a net worth of US$2 million or more as of the expatriation date." That's not liquid net worth, or realized net worth, it's just plain old net worth. If you are subject to the tax, all your assets are deemed sold as of the date of expatriation as income tax on the phantom gains are owed.

Of course someone could hope to stay off the radar or move to a non-extradition country and try to thumb their nose at the USG, but there's a big difference between a loophole existing and the fact that enforcement isn't always perfect.