You yourself write here that deposits with deposits in bitcoins will be very risky. Especially on such a risk banks will never go. They do not like to take risks. They have something to do without such a degree of risk. Bitcoin has already reached its high cost and its further growth will be doubly risky. Banks will not exactly take bitcoin in a deposit at interest. They know how to calculate their benefits, and this activity will be unprofitable.
I don't think banks will offer bitcoin deposits because it will take away the decentralization of bitcoin. Once we deposit our bitcoin to the bank, they are already in control of our coins so anytime they can spend it or in a case when the bank's wallet will be hacked then all our coins will be gone. That's why there is a concept of being our own bank because we don't need the banks for our coins to grow in value. Besides that, given the fluctuation of the price, I doubt they will be willing to take that risk.
I think banks today should consider having cryptocurrency as a deposit but for now it is quite difficult to implement it and at the same time it is difficult to convince banks today because of the decentralization of cryptocurrency and of course they want to have a guarantee in any money or coins they will allow in their bank.This is the best marketing strategy that can be done by the bank. To offer or add their services in crypto. If they do this, I think banks have the opportunity to develop and develop client needs.
Maybe the option banks would have is to become the gateway for the conversion of crypto to fiat or vice versa because it is an undeniable fact that fiat is still the legal tender so we still need to convert our coins and if they offer such services for a fee then they will profit from it but then as I can observe, some of them are against it because once they track that an account holder is involved in cryptocurrency then they will suspend his account.