Just his opinion about bitcoin but i dont think that will happen, fiat is something that can't be replaced cause of it's history. Things that you are using daily and it's need much time to change it. So if this happen , i think the next 100 years maybe ?
Even in the next 100 years, I do not see it happening. Over time, technology may evolve, older folks get bounced, more of the new folks who are more technologically oriented move in to the scene and we may see the lesser use for paper currency but that does not mean that government controlled fiats would not always still be in existence and bitcoin can and will never be an alternative.
Yup, maybe the world will change to use digital currency or digital payment method, but the paper money function gives us is indispensable. No digital technology can using without internet. But with paper money we can use it for anytime, even we are staying in countryside.