Anything could happens in the future, if we see from what's going on in crypto world nowadays was very surprising , where most country using the crypto system for their economy and it works. I think it would be possible to change the real money in the future and using this awesome thing as the transaction and a payment tools instead.
If you are talking about the impossibility of crypto replacing fiat, I guess that is understandable, because I actually do not see that happening either, considering the fact that crypto space will just be an alternative, and in that case, we will get to see coexistence.
However, if what you are talking about physical cash not being replaced, I am sure you should have notices generally in most parts of the world now and most especially the developed ones, that we are actually hitting the cashless age in which everything gradually becomes digital, and that is how i see the future of money, in a way where everything is digital and not physical.
[bif i see lately there are lots of altcoins popping up, especially in the digital world and whether for the next few years the function of real money itself will be eroded by the presence of virtual payment equipment ...? I had time to think whether in the next few years we would be making virtual money payments ...?[/b]
it seems that it can happen, at this time almost all countries emphasize non-cash payments, so the use of real money starts to decrease, this is very positive for a country because it will reduce government spending to pay the real money printing costs
In fact, in my country, I often do not hold cash and that is practically because, I realize that most times, I usually do not always need it, considering that I always get to pay most of my things using my card, so in that case, that is all I need in my wallet to be holding around most of the time which is exactly how I see the future of money.
Now that things are even getting a lot more interesting with cryptocurrencies, and the avenue with which rather than printing money, governments all over the world can now integrate the blockchain technology, it seems at the long run, digital money will become the future of the way we spend.