That will not happen. But I think that will not happen so fast. That is not so good for the people.
I think that more people will use also normal banks. And they dont know how to use Bitcoin.
To some extent the world is ruled by banks, in short the government and if bitcoins take over banks then the government will lose its stability and I do not think the government would let a decentralized currency get the better of them.
The banking elite is controlling the world. Not just financially but also politically.
If you think about it, most of the things go through them, which makes them impossible to defeat.