A decentralized bank? Banks are meant to be centralized and AFAIK there were already few of them that operates now. What will be the purpose of crypto banks? we can save our own crypto's with our own wallets. In some of their service, they lend money so that's going to be one of the feature that they can offer? lending crypto's to their clients.
Reading the OP's post I have this same questions as bhadz before I even read his reply.
What do they get from just being a bank? And you are saying a decentralized one?
I dont think so. There will no profit from it. Who will create a non-profitable business? Only martyrs will do. They aint satoshi.
Obviously, they will need something to work it out. A trading platform maybe inside a banking system which is decentralized. But it could be risky.
Why them, if we could stay with other trading platforms out there.
Too many questions going out of my mind. Can't answer the question of the OP.
All I know is there is no need for Crypto Banks. Just dont be lazy keeping all your private keys or writing it down with instructions in case of your death.