Start at a value that is truly eye-watering for your average citizen, one which the lower-99% will never reach in their lifetimes. Say, for argument, $10M.
Implement an algorithm that plots out a Sigmoid Curve - 0% taxation at $10M, and increasing slowly at the beginning. Once it gets close to the inflection point, it rises rapidly to over 80% taxation, at which point it then slows down again, reaching 100% taxation for everything above the maximum value.
Which would be set at something truly ridiculously high - say, $100M.
That way, we have a smooth curve that cannot be “gamed” anywhere as easily as abrupt taxation levels. And we use simpler, market-valued assets from anywhere in the world that focus on how the hyper-wealthy sock away their wealth.
As such, any sort of classic investment is most definitely on the table, especially if it is ever valued by an open market. Housing, land, gold, stocks, bonds, business partnerships, you name it. All on board for taxation.
The nice thing about Sigmoid curves in a taxation role is that they start off incredibly gentle - you will likely not may much tax at all until you hit $25M of net worth, because it’s paid progressively on any amount above $10M. But at the same time, you pay 100% taxation on any net worth above $100M.
It is truly a progressive tax, leaving plenty of room for the ambitious, but is punishingly draconian on the vampiristically greedy.