> ... when there isn’t place in the real world even for the largest one?

Uh, go visit El Salvador. Every MacDonalds, every Starbucks, and tons of local businesses accept "the largest one." That's because bitcoin stands apart, in terms of its real decentralization, and therefore its independence and utility. Give it time, and it will become far more useful than it already is. The dollar may eventually refer not to a specific weight of gold (that's what the term 'dollar' originally meant), but to a specific number of satoshis.