I think there will always be a need for fiat. The concept of fiat itself particularly the cash representation is a great concept if not for the fact it's controlled by money printers. Cash is private and will be still be a valuable medium for exchange within countries, but yes cash itself will not be the 'value' of the future, it will be only a medium of representation of value against bitcoin in my opinion.

One would expect XRP is going to become an even bigger player in the crypto utility space and it wouldn't be too far fetched to expect a marketcap that will eventually run into the trillion/s mc space.