This doesn't totally sound like a dream. It sounds like a possible utopian future, given that blockchain tech has developed a lot and lot advanced these days. Anyhow, even though it might seem possible for the entire world to use blockchain as its main system, it less likely to happen in our timeline. Decentralized government sounds illogical for the most part. Our species is a greedy one. We also want more and more power. If it's possible, each of us must have the desire to rule the world. There's where this system won't work out given the circumstances of this era. In conclusion, it is not impossible, but it is just less likely to happen soon in the near future.