Absolutely... market depth wouldn’t come close to supporting selling that much ETH without dropping the price. Markets would also react quickly on the news that the balances in his wallets were changing significantly.
Saying he isn’t a billionaire because of that is sort of a double standard though. Most billionaires don’t have billions in liquid cash, they almost all have illiquid property, stocks, bonds, etc. Selling off some of these assets would cause a very similar effect, and often they can’t easily be sold at all.
There are full fledged wall street trade desks that handle buys and sells in large amounts using same day wires, they would get ethereum and he would get USD, and "the market" would never know.
1.1 billion would take a few days, but it would be shopped around to other firms that want to buy that much without moving the market.
OTC markets would probably price his assets at a much lower value than current trade price because of the volume and reaction from the markets. Public would know because the only way to safely trade ETH without letting Vitalk continue to have access is via a transaction, which is publicly accessible. I don’t know if his wallet addresses are publicly known, but a $3.5 billion transfer wouldn’t go unnoticed. Markets would almost certainly react negatively to him liquidating.
That said OTC price of everything could still be over $1 billion.
People don't know Vitalik's addresses. People estimate his worth and have no idea how much he kept or sold after the ICO in 2014 or at low prices in Ethereum.
Also, Ethereum won't mix inputs from different sending addresses, so it would have to be done in multiple transactions if he has multiple addresses. This would be indistinct from all the other transactions on the network.
OTC markets would try to price his assets at a lower value, and thats where you negotiate, and find counterparties yourself. If you know of several hedge funds that want to BUY ethereum without moving the markets UP, then you can sell straight to them, and tell the OTC trader that they won't get any volume and then you'll get a better price.
Saying he isn’t a billionaire because of that is sort of a double standard though. Most billionaires don’t have billions in liquid cash, they almost all have illiquid property, stocks, bonds, etc. Selling off some of these assets would cause a very similar effect, and often they can’t easily be sold at all.