The number of people using it by 2022 will be more than double compared with today, but it would still be only a relative fraction of normal currency users.
Bitcoin will terminate the fiat system. It may not the coin itself but the concept of digital currencies is a very powerful one. With the growing technology, everyone wants to do all tasks with the help of gadgets that simplify their work. Digital currencies are more easy to use than fiat and bitcoin is the best one. Once accepted everywhere, the use of fiat will start decreasing.