I'd say that I'm a critical believer..Bitcoin has a great potential for the growth and it'll become commonly used in 5-10 years (hopefully), but it definitely won't be the reason for the fall of government fiat currencies
Even for 20 years I can't see bitcoin will replace the whole fiat industries.
In my own view, I don't want that to happen. Im happy with the current usage of bitcoin now. Development must not include replacing the whole fiat.
I have my own reason why I don't like bitcoin to be the main currency. Im happy how bitcoin works today. Taxes here really sucks. You can understand why Im saying this if you will experienced where taxes here go.