3% annually would be really huge, and probably shrink a lot of personal wealth out there. 3% one time is not as big of a deal, but it also doesn't raise so much revenue. The problem with a one time wealth tax is it incentivizes a future government to try a second one-time wealth tax, and then maybe a third. Soon enough it's not really a one-time tax any more.
In the United States there would also be a serious question on whether wealth tax was constitutional. The income tax was not raised until the 16th amendment explicitly gave Congress the power. It's possible the court will say there's no power to levy a national wealth tax absent an amendment.
I imagine a realistic implementation would involve a system of progressive brackets and minimums/deductibles, modeled after the way income tax is. Ideally, things are modeled such that the tax is only full percents among those absurdly high brackets that can afford them
Constitutionality is another matter though, and yeah it seems like it would be awful hard to get that through the current court