Any global currency not overseen by a central or distributed (stakeholders) authority needs to be based on some sort of work to be scarce and neutral towards all the participants. I believe Bitcoin is a pure form of money in that sense.
The next step is getting rid of resource scarcity through technological advancements, in which case the idea of "money" and "economy" as a whole may no longer apply. How long will it take? Time will tell. But we are getting there
.But why do we need a decentralised system. I'm sure there are some people out there who don't trust banks and support btc for this reason. But the resulting technology has resulted in a system that makes it easy to buy drugs and launder money. I think the vast majority of people want to be able to make safe, reliable payments electronically where they don't have to gamble on exchange rates or being ripped of by exchanges. Having a decentralised system has not achieved
My vision is that it needs to grow into something bigger. When it is used by nation states as a global settlement system, then we can judge how useful and successful it is. We are still at an early stage right now.