The title of your story is hardly believable. Associating banks with any kind of rags to riches story is beyond most folks credulity I think.
Most individuals given the choice will continue choosing to be independent of banks, and for sure the scaleability issues you mention, where they still exist, will be overcome.
Where banks will probably always have a role is in interfacing profit driven business with what is already a massive new worldwide market of crypto-currency enabled consumers.
Large profit driven entities, and regional governments are centralised by nature, whereas individuals are evidently drawn towards decentralisation.
There needs to be an interface between these two worlds, probably formed by an intermediate layer of closed permissioned ledgers, rather than the open distributed ledgers delivering to people the freedoms they obviously want.
There seems to me to be a very large body of misinformation going around, that distributed ledger somehow empowers business, including banks, to increase profits, when in fact it does not.
As far as I can see, all it can be used for is to give business side-ledgers which can be meshed with the larger worldwide distributed ledgers which are currently empowering people to be independent of banks.