I expect longer than 20 years. The majority still believe that fiat is very important in their lives. They continue using it and continue rejecting the potential value of bitcoin. I don't wonder why it will happen because not all will be able to see the future fiat collapse, which leads them to think they need to take action now before it is too late.
It remains an option for everyone until they find out that it is necessary to secure their future and assets and make no choice but to do it. It all changes when facing the situation.
Also, I think it's going to be a gradual thing, over 10 years for example.
Kinda like what we've already seen from Genesis to today, a gradual change, with some big events in between, but in general Bitcoin has grown from almost obscurity to mainstream.
And right now there are 19M+ coins of the 21M in circulation already, so it's going to get more competitive over the years.
