> households worth more than $100 million would pay an annual minimum tax worth 25% of their combined income and unrealized capital gains.
To be clear, Norway has also had a wealth tax for years. Summarised: The wealth tax rate is 0.7%(local)+0.3%(national) and is calculated based on assets exceeding a net capital tax basis of NOK 1.7 million for single/not married taxpayers and NOK 3.4 million for married couples. (Ref: https://taxsummaries.pwc.com/norway/individual/other-taxes)
And regarding "taking out loans against their own share portfolios": Yes, I agree, this is genius tax avoidance strategy. And, I am pretty sure the interest paid on that loan would be tax deductible in the US! Most large investment banks have a separate trading desk that facilitates these loans via private bankers.