anything that tries to separate bitcoin and blockchain and only take the blockchain (the technology alone) is considered an altcoin which has nothing to do with bitcoin.
and all the banks doing it are creating a centralized altcoin which is way worst.
It will still be usefull for their internal systems and handling of transactions. A chain like that does not need to be decentralized or public. It would just run their systems in the back. Nobody needs to know it is being used, the same as current architecture.
With the current hype to start investigating blockchain though, banks will probably be showcasing with it and promoting that they are using blockchain tech to revolutionize the way of banking (which does not change ofcourse).
Banks will never use bitcoin, billion dollor companies wont rely on systems run by others. It is just not secure enough.