People's belief in value
"as with all cryptocurrencies right now, its value is nothing but perceptual. There is literally nothing to stop being worth $0 beyond people's belief that it isn't."
"the illusionary foundation for its billion-dollar business that comprises of nothing but others' confidence that it is worth something"
To be fair, the value all fiat currencies is perceptual, and based only on the belief in it's value. The difference is - what is the belief based on? If it's USD, people have considerably more confidence in it retaining it's value than in for example, the Zimbabwean dollar or Venezuelan bolivar. In the case of a cryptocurrency, the belief might be a bit limited in scope, but it can be fervently religious, which is about as strong a belief as you can get.
" $4bn in cryptocurrency. Investors used one cryptocurrency to buy another cryptocurrency and then Block.one used a wildly varying dollar-to-crypto-coin exchange rate to state its value."
True, cryptocurrency valuations fluctuate wildly. However they don't fluctuate THAT wildly that a $4bn valuation can be pulled out of a couple of bob. People spend 'real'* money to buy their cryptos, and, the 'theoretical' valuation of a cryptocurrency IS actually what someone is prepared to pay in real money for them. So the fact that the $4bn is in cryptocurrency doesn't take away from the fact that a lot of people poured a lot of money into this company. So maybe if they try to cash out their invested crypto and only get 10c on the $, it's still a hell of a lot of money to be spent on, what, as you correctly point out, is a company that seems to have no assets beyond the newly bought website, and no revenue stream.