I'm not saying I agree or disagree with this stance but at a practical level it's interesting to think about.
Let's say life is a computer game, and once you max out at $1bn in earned wealth (presumably this includes liquid and illiquid assets such as properties, cars etc), you cannot accumulate more wealth.
How does a government enforce this stance? You cannot stop say Bill Gates shorting Tesla and earning millions from the trade, can you?
Can you stop a landlord renting out their properties to block further income from them?
What about interest generated from bonds or savings accounts?
Do you simply tax the shit out of people if they have over £1bn in wealth?
The big challenge I see for all of this is that rich people have the best (and most expensive) accountants/lawyers money can buy. If you try to tax the shit out of them, their accountants and lawyers will find a way around it.
Also, if one government is too heavy handed, they'll just move assets to another more lenient government.