You mean as global store of value or actual day to day transaction for something like bitcoin ? The first seem to already happened and the second quite unlikely (for bitcoin maybe if something build over it do the heavy volume and low cost required).History books make revolutions come across as events when they are actually processes. We're living through one right now. This is a 20-30 year process that will culminate with Bitcoin (or Ethereum as a darkhorse candidate) adopted as global money.
Are we not already somewhat past that in some sector, an Argentinian can buy an house-appartment with bitcoins and other crypto, which create I could imagine a big enough market to be useful too some even if they themselve could not transfer it, has long has they can buy their next house using the crypto gained from the sales of their previous house.It falls apart when reminded that all magic coins eventually have to be converted to fiat currencies in order to hold any value. If you can't convert it is worth nothing.