Banks would never switch to a system that makes all transactions publicly traceable, and they shouldn't.
The industry has investigated blockchains for many years, since distributed consensus for transactions is a problem they actually have. They might run their own private chains. But it won't be ETH.
Conceptually, a service provider utilizing Ethereum could create or aggregate on-chain services and package them in a similar format to what a bank is today with very little overhead.
I heard exactly the same said about AWS in 2009, now almost every major bank uses it. Once something is shown to be more efficient those banks are going to have to adopt it or justify their inneficiency to their shareholders.
Lots of companies released blockchains and coins. It's called FOMO, or "Metoo-ism". Interpreting this (or IBM's blockchain) as signs of a significant market shift is a triumph of hope over realism.
It won't be public and it won't be distributed - it would quickly revert to some form of centralized piece, hopefully one at each bank, but will probably end up with one huge central point. They will still call it blockchain to attract gen z to work there, but behind the scenes it will work just as badly as the current mess. It's in the bank's/banking industry's blood and regulations to centralize. Whatever gets thrown their way will get locked down and centralized. I can just imagine the huge audit systems that will spring up to audit the blockchain (where ideally you wouldn't need to audit it to begin with, just look at it cause all the same info is in front of all parties, unmodified). Nightmare fuel actually. Better just to start from scratch (new banks, new core banking software, different kinds of audits and regulations).
The industry has investigated blockchains for many years, since distributed consensus for transactions is a problem they actually have. They might run their own private chains. But it won't be ETH.