This is directly addressed in the article. Unrealised gains can still work as collateral for loans. The spending habits appear as if your unrealised gains were bonafide income. At what point does the distinction between wealth and income become arbitrary?
There seems to be a large amount of "missing the point" in this thread. As a wage labourer my wealth growth is significantly hampered by taxation. For the small group of people with net worth tied up in financial assets, taxation doesn't slow their growth in any meaningful capacity. If we ignore any ideological predispositions and instead simply ask what limit this system is approaching I think the answer seems terrifying.
A common sentiment here is that inequality is not a problem in and of itself. "How does Bezos wealth possibly impact me?". Having seen the difference in equality in Scandinavia, USA, and South Africa I would beg to differ. Inequality eats at a society at all levels. The rich I met in America seemed less happy than the poor in Sweden. In South Africa even more so.