There are many reasons for a currency to exist, first we need a new currency because we need to use it for our specific purpose, like we want to use that currency for banks, we use banks currency, but not all currencies are successful despite how advanced they are because they can not be applied in the real life.
Soon all using FIAT currency will be replaced by Bitcoin.At first it will replace the dollars,then followed by all the fiat currency.Do you know many online transcation are accepting the bitcoin as their one of the cash.This is the first step for growth to bitcoin.It may be a first step towards the success.