Somehow they can do that, if the trend became the essential in the future like todays fiat money maybe they will create a crypto that will be the flag bearer of a particular county in crypto world and I guess bitcoin will be the international monetary for cryptocurrency still.
They have the power to do that but they won't gamble their business to something decentralized by adopting a coin that they don't have the authority to control it.
They can create their own cryptocurrency but it can be a stable coin which is not volatile for the sake of their business and customers. It will be a digital currency if they do that but there's no need for them to do it, they have online banking and adoption of blockchain is what they only need to do.