While I think "digital money" will replace existing currencies eventually, I don't think there's any reason to believe our first popular cryptocurrency is necessarily the ideal solution. There'll be better currencies that come along and replace Bitcoin (faster, more secure, more anonymous, more energy efficient, etc), and the world will coalesce around one of those.

However, before any universal replacement of money with a cryptocurrency can happen there are some huge problems to solve, like the fact that fewer than half the people on Earth have access to the internet right now. We can't possibly have a global electronic currency if half the people can't use it.