The most realistic outcome in my opinion in terms of mass adoption is that people see bitcoin as an alternative, or parallel to the fiat banking system. Some may even choose to use it exclusively as people already are doing now. But a decentralized crypto completely replacing fiat seems like a far fetched idea for now.
We even never thought 80% of people in the world using smart phones before 10 years but now it is the reality so when people starts to accept it then it will move to mass adoption because people were most likely ship they just do what other were doing.
