This kind of thing is making me think that more effort should be made for realistic land/property taxation; not only is that where a lot of the wealth ends up being kept, but it's fundamentally impossible to hide.
It needs proper cadastral property registration and a link to the tax system. It can even be privacy-preserving; the system doesn't need to care who owns the land, just that the taxes are paid.
For the UK I'd happily swap out council tax + stamp duty for a 1-2% annual property tax.
You might have to rethink your math, here in the U.S. property taxes average 1.15% already, and would need to go up to like 8.2% just to account for personal income tax (not including payroll taxes, social security, Medicare/Medicaid, and corporate taxes)
I think the point is to tax land value, not land. You can buy well over ten thousand acres of land in the highlands for about $5,500,000 (i.e. the price of a really nice house in London) [0]. It's an enormous amount of land, but you can't really do very much with it so the value is relatively low.
It needs proper cadastral property registration and a link to the tax system. It can even be privacy-preserving; the system doesn't need to care who owns the land, just that the taxes are paid.
For the UK I'd happily swap out council tax + stamp duty for a 1-2% annual property tax.