One day banks will accept Bitcoin as medium of exchange and accept deposits from bitcoiners. As soon as the world powers accept it as medium of exchange.
I think it will take about a decade for banks to start having a large amount of bitcoin as reserves.
The "central bank of central banks" already allowed central banks to have up to 2% of their reserves in bitcoin.
That's a massive change in how banks work, and I can assume this will only expand over time.
2% is still pretty low if we compare to the bank's gold reserve but it's a progress regardless.
If they accept crypto deposit however, this number could jump up and who knows regulation cater to the demand and increases the allowed reserves of crypto.
What it needs is just one bank with crypto deposit and hype. The other bank will follow later.