Blockchains don’t really let you do anything useful that you couldn’t do before. But they make some things much easier and more accessible, by a big enough margin that they unlock some kinds of broad experimentation that weren’t really feasible before.
Take what I assume will eventually be a category-defining use case, “Facebook, but owned and governed by its users.” With some imaginative lawyering, you could build that in a durable way today. But it would take capital and know-how most kids in dorm rooms don’t have access to. It’s like how the launch of AWS didn’t let you do anything that was _impossible_ to build with on-premise hardware, but it unlocked a lot of innovation anyway.
Right now Ethereum is a very shitty version of Lambda plus DynamoDB, but with some interesting primitives around payment, ownership, and governance baked in. I actually have very little faith in the Ethereum roadmap given some dabbling I did in it a few years ago, but there are competing protocols with much much better performance and developer ergonomics, so they’ll either catch up or get replaced like a bad operating system.