Crypto central banks will work in a way like it may use bitcoin as a reserve and may not use bitcoin as a momentary unit. At the same time this does not mean bitcoin is going to give room for altcoins to be used as a money because bitcoin-lightning kind of new innovation will do that job as may not be recorded into blockchain for every transaction but may hit blockchain once in a day as it may happen in very less value.
Yeah, the reason why there is always an alternative is so that when some people decide they don’t like the real one, they can go for the alternative. But just know that alternatives can hardly be as good as the original. I do know that there are good altcoins, but a lot of them, from what I have noticed are centralized.
Just look at Bitcoin for example, there is no central point that controls it, it is completely decentralized and not being controlled by anyone, but most of these altcoins has a place of control. So that means that they are not fully decentralized, though they might claim to be that.