I think CBDC proponents want to create their own system of international financial settlements, independent of the US dollar (as the global reserve currency). It's just a very complex and lengthy process. 🙋
And you're absolutely right when you say it could take decades. First, CBDCs must be fully implemented in these countries. Only then can their central banks begin to consider unifying the international use of central bank digital currencies. It's a long process.
At the same time, the very creation of a CBDC precludes preserving the invariability of the US dollar. The old financial system based on the US dollar is crumbling before our eyes. Why is this happening? The point is that once the technology is created, you are forced to implement it, otherwise you will begin to lag behind the leaders of civilization. This is precisely why the US is now legalizing stablecoins.
So, the answer to your question is yes, the US dollar will gradually lose its position, while American stablecoins will gain wider adoption. For example, Iran is already actively using USDT to collect fees for ships passing through the Strait of Hormuz. This seems surprising.
They are not going to just stand and wait around for decades, they will do some other stuff while doing CDBC as well. But it is clear that the world is tired of the USD market covering the whole world and the yare selling it from their treasury as well.
Bitcoin in fact even plays a good role in this, there are many nations who sell their dollars and get bitcoin instead, not a lot, just a few thousand for now, so a small number, but in the end, all of the nations how had huge dollar number in their treasury is looking for a way to get out because dollar has been devalued way too much, and they have way too much debt for the future which makes it look like not a good idea to keep it for now. If USA gets better in near future, maybe it will go back, but right now it looks bad.