10-20% adoption rate is a very optimistic and positive scenario. While I'm more than sure privacy and decentralization is something people will look after in the future, I'm not sure 1-2 out of 10 people will be looking for it. People seem to choose convenience over self-custody more than ever before. It's the age of technology where you literally ask a random server owned by a stranger to tell you what your To-Do list is for today.
We can barely predict an approximate price for the first day of 2021, let alone 30 years from now. If the governments only keep powering up their fetish for control and power, Bitcoin may have to go through some hard times before succeeding as a
legal peer-to-peer currency to use. From what it looks, the govs only keep geting more and more annoyed by the idea of letting their citizens be under control of their own assets.
Agree, no one can tell what will happen in the future 100% correct, but we can speculate based on probability and mathematical calculations, such as people predicts bitcoin may reach $20k in 2020, well it might become a reality by the end of this month. Bitcoin growth is influenced by several things, such as halvings that affect supply and demand, trends in the market, regulations, adoptions, etc. If bitcoin can reach $100k in 2021, it's not impossible to hit $1 million in the next 30 years.