I don't think it will take 20 years. That's too long of a timespan and the world at it current state is too fragile. I think we need a few (maybe just one) major catalyst event in the financial sector to draw people into decentralized financial solutions regardless the ease of use. If people see the value higher than the ease of use then it won't be a problem. I do agree that some level of centralization is good at least right now to make things moving but in 5-10 years it might change.