That is not going to happen in the near future. Central banks have an easier time backing it by gold and are not doing so although China is rumored to be planning to do so. Bitcoin is too volatile as of today for it to serve as a backing.

What would not surprise me at all is if some countries decide to start mining Bitcoin. I think that will happen before they dedicate to back the currency in it, if that ever happens.
These are ideas that might seem far-fetched to many people today, but how gambling with Bitcoin might have seemed 13 years ago, and we see how important it has been in the history of Bitcoin.