How would this work with real-estate? Probably the Y that should be taxed the most when we're talking about wealth.

Rich people are very good at coming up with ways of financializing assets to their advantage. That creativity goes away when it comes to paying taxes, for some reason.

Real estate mostly isn't subject to the "I sold one for a huge sum, but the price would tank if I sold them all" effect, unless you own immensely much real estate.

But either way, just a lien on sale of the properties. We can still give the option of paying wealth tax according to valuation directly (in $) instead of in natura (in Y), then there's less to complain about - and as a bonus, we get revealed preferences on how inflated people think the prices of their assets are.

A lien on the property? Although almost all jurisdictions already have property taxes, so it hasn't been an insurmountable problem so far