Of course it can't. Bitcoin is not accessible to all people specially the people who live on below poverty line. Value wise it is the most expensive currency but imagine going to the store buying things using bitcoin and waiting for a transaction to be confirmed. Hell no.
What are you talking. If the price reaches the value of 10k $,bitcoin will replace the dollar. FIAT of various type.First one is dollar. At first bitcoin will replace the dollar and follow by Euro and so on.But it takes some time to make replace the FIAT. You can trust bitcoin ,it will replace FIAT.
Dude is this really your account? There is no way a crypto-currency will replace a fiat. Let us all be realistic, it may sound nice but be realistic, even if the price goes over 10k it will never be accessible to all. The higher the price of bitcoin the harder it will be accessed by everyone. People with knowledge and being familiar with bitcoin does not mean they are with it.
Bitcoin is going to be the only international currency in the near future but as far as the replacement of fiat is concerned, as long as we have poverty in the world and illiteracy fiat is going to stay in the world because these people are unable to understand complex methods of using operating these currencies. Bitcoin at present is limited to those who are educated but not for those yet who are illiterate.