If I'm honest I do not see this happen in the future, the banks are just to big if you compare them with the bitcoin.
Also the fact is that a lot of people are depended on a bank nowadays so its maybe possible in about 10 years from now on.
Even after a decade I think there will be many people who would continue to use banks, as they find it easy and convenient and banks are also involved in providing best services to their customers, so if the customer is satisfied with the services he will never switch to bitcoins.