Banks use tools as a store of value by holding some assets in reserves, for various economic benefits. Although, adopting Bitcoin in such capacity, would have it's pros and cons. Obviously like controlling inflationary trends, and even help stabilize the volatility of Bitcoin to its users, and conversely such volatility could also alter the stability of a banks statement of financial position. All these could add up to a more stable global economy. Surely banks have started to think of such prospect
This is not as easy as you may think in theory. Banks can't decide its monetary policy in full because it always depends on the legislations from which it took its activity license, except for frw online virtual banks who has already started accepting crypto payments such as Neteller and Skrill. I don't know if in any legislation worldwide there are banks who have the ability to accept bitcoin as a value asset and add it to its reserves.
Let us put it this way, every Central Bank has its own protocols and so crypto regulations may vary from country to country. Thus, we don't know exactly their regulations when it comes to crypto. But right now, we are seeing that some Banks/Central Banks owned by the government are publicly stating their stance towards btc or crypto in general. And most of them are positive on this market.