It is not of any importance for bitcoin to surpass the fiat currency cause they are two different coins/assets with their own features and importance from their different use. The use of bitcoin and its wide adoption as the number one crypto currency, for it to be brought down to local currencies or for one to make use of it locally the use of USD fiat comes in to have its play in the exchange as a standard for international exchange converter. In most countries that is not yet endorsing the use of bitcoin as a means of payment will want to convert their bitcoin to local currency I other to complete a transacr. So, in every way they have their functions and no one can take the place of the other.