We need something like:

• Unrealized gains are not taxed directly (because that does create issues). But borrowing against them is treated as partial realization, which is taxed. Loans shouldn’t be a way to live without a tax burden. Tax the collateral as a percentage of its value.
• Maybe put the tax on the loan issuer, who can then determine whether or not to raise the loans rates or add fees to offset the burden.
• Instead of taxing gains equally, tax assets according to how liquid they are. Public stocks are high, treasury bonds are high, private businesses are low, primary residence is low, fine art is low.
• Deferred gain with interest. Gains still accumulate without tax. When eventually sold, you calculate interest at sale time. An interest surcharge is added based on how long taxes were deferred.
• Allow equity dilution: Instead of requiring cash, large holders of public companies may periodically transfer a percentage of shares to public treasury.
• Tax luxury expenditure derived from wealth. Private jets, yachts, a fucking social media company… tax the shit out of stuff like that. Use market rate as basis. If a company buys a yacht to lease to the CEO, the company pays the tax.
• Tax publicly traded assets via central clearing systems, on a rate to scale basis. First $50M annual exempt. $50M–$250M tiny rate. … $100B+ steep rate.

You wouldn’t even have to worry about dynastic wealth via step up in basis, after a certain point. So long as you’re effectively taxing wealth along the way.

Honestly… you know what the billionaires say, right? “Move fast, break things.” I wonder how they’d like it, when it’s their things which might break.