I am pretty sure cryptocurrencies will replace fiat in the near future. I dont think it will be BTC or any other decentralized cryptocurrency.
It probably will be a coin "based on blockchain technology" which wont be decentralized and will be in "full control" from governments/financial institutions.
Like russia started to roll out the Crypto Rubel.. i think a lot of countries will follow soon.
I hope they wont see BTC as a threat to them and start banning it everywhere.