Indeed, even for us that bitcoin seems a popular currency and it is a great investment to put our money but for most of the people in the world, it is not an interested topic for them to buy bitcoin and consider it as a legit investment because for them, bitcoin is not worth it because of its fluctuations which is wrong and even bitcoin cannot replace the fiat money, it can still be adopt by a lot of people and the majority of the people in the world just need some orientation so they can learn and understand bitcoin.
It is still hard for bitcoin to replace fiat because many people don't even have access yet to the basic tools needed to transact using bitcoin. People need gadget, electricity and internet connection and there are so many people who have no access yet to this kind of necessities. In developing countries, some people don't even have electricity so it would be hard for them to transact using it. More possibility is that they don't even know about it so it would be kind of hard for bitcoin to replace fiat during this time.
The only option I can see for bitcoin now is treat it as a store of value along with precious metals and commodities as many are saying its kind of expensive to transact small value transactions so having it as an option for long term investment is a good way of using it. Maybe it cannot replace fiat but it will co-exist with it along with all other cryptocurrencies.
I agree with you that it is very hard for bitcoin to defeat fiat completely because mostly of world population are poor and illiterate. People of third world countries are still deprive from electricity and are still even seeking for food so how they can access to bitcoin even to understand bitcoin. Under-develop countries are also facing lake of electricity problem, lake of computer knowledge and facility of internet. So it is right that in near future bitcoin cannot replace fiat.