We as Bitcoin supporters really expect banks to adopt Bitcoin, but as we know banks need government approval to be able to adopt Bitcoin.
Banks do not expect decentralization in their financial systems, but we can expect them to provide services that support users to buy (deposit) and withdraw profits from trading to fiat through their services. So don't expect them to adopt bitcoin.
As we know, banks were established with the government's permission to carry out their services to assist the community in meeting their daily financial needs. It is natural for them to comply with government regulations if they want to continue to run their services. But if the government has given the green light for bitcoin, then we can expect something good for bitcoin adoption in the future.
So it's impossible for banks to adopt Bitcoin right now. But don't know what will happen in the future, there is a chance the government will change its mind and allow banks to adopt Bitcoin. Although the possibility is very small to be true.
The only hope to get the government to change the regulation is for western countries to start adopting bitcoin as a legal tender or currency. But as long as western countries don't do it, then there is little possibility of legality.