Then why do you say it if you don't know at all? Do you at least have a link that backs up your assertion?
This is nonsense. How many kiddos are out there who loaded up on cryptos and held through all that volatility? Hardly anyone. Those few who sit on sizable gains can only live in and own that many houses. Your suggestion does not make any economic sense.
Market cap has nothing to do with it. Market cap is different for each legal tender currency thanks to exchange rates. It must be looked at in your home currency. For now, crypto is nothing but an asset class no different than stock, real estate, collectibles, art, metals, cash, etc, etc. Some people think future returns on crypto will be the same or greater than they can attain from another asset class. Those same people buy and wear shoes.
I am saying this, despite not fully knowing, following logic, common sense and basic sovereign regulations around internal trade. If a country constitution defines a certain currency for the sovereign state, domestic trade is usually not allowed to be conducted using any other currency, unless explicitly permitted by the state, either in general known situations (For overseas customers) or for specific situations where the corporation gets written approval to sell it's goods & services in a different currency for valid reasons which gets approved by the relevant authorities/regulators.
You specifically mention internal trade, however, you've described a barter transaction. Im not certain, but unless the sovereign state acts as an intermediary, the state has no input when both parties are in agreement to the transaction terms. 1 chicken for 1 pair of shoes.
Where I live in Europe, foreign currencies (so any other currency or crypto) can be refused as payment. Only if both parties agree another currency than Euro's can be used. I know that in gold, copper, lead... many contracts are billed and paid in USD. The reason is that these materials are quoted internationally mostly in USD. Using other currencies too, would complicate the hedging of the contracts as there are price variations in these commodities (hedged on the LME in London) and there would be needed an extra hedge for the different currencies.
Fiat currencies actually mean that the courts will adjuticate based on contracts settled in USD. IT also means companies in the US MUST allow anyone to buy in USD - they can't refuse that method of payment. But they can accept another if both parties agree.