What you said it is correct but we are still very far to reach that point, when the dollar falls of grace as the world reserve currency the next question is what to do then, and economist have suggested what you are saying using a basket of fiats and creating a new world currency as a result, so what you are saying makes complete sense but you are too early, I do not think that is going to happen in decades or even in 50 years.
To be blunt, mainstream economists have mainly existed to serve the ruling elites. They were in favor of the gold standard when it was operating, but are now almost totally against it. Both times, they were saying what the elites wanted to hear, at the time.
World reserve currency is essentially a bubble that is propped up by the elites. The nature of bubbles is that you don't know when and how it will collapse, but you know it will, and that you know the elites and their mouthpieces are always going to be saying everything is fine, before the collapse. So accurate information of this nature is hard to come by.
It is also possible that the emergence of Bitcoin has given the elites an opportunity to deflate the bubble preventively. Something of that nature happened around 1985 when a hard landing of the dollar was prevented by a combination of talking the dollar down and forcing Europe to inflate and making their currencies unattractive.
A basket of fiat currencies is what economists always talk about (assuming you mean the SDR issued by the IMF,) but we have no history that shows success by a reserve currency issued by a centralized authority without the help of a unified imperial power. Through 500 years of modern history, global imperial currency has always been a combination of state issuance, precious metal backing, and support by imperial power. Over the last 45 years the currency itself went totally fiat, and I don't believe this condition can last long. Of course, the politicians, economists, and bankers are always going to say it will last forever.
Do not get me wrong I know they are bought, I was just pointing out the direction they want to go, and we may show to them that has never existed and that is not going to work but those people always think they know better, in my opinion there are only 5 scenarios possible
In the first scenario, there is no reserve currency and each country tries to hold the currencies of other countries similar to what China and Russia are already doing, in the second scenario a basket of currencies is created and a new world currency is created, neither of these scenarios are going to work.
The third scenario is the one you presented in your first post, the fourth is going back to gold and silver and while you believe more in this scenario what it is going to happen when we get access to the technology to explore the space and get as much silver and gold as we want? I think humans will have at some point to create their own scarcity somehow and bitcoin show to us how we can do it.
And the fifth scenario is chaos, which is terrible but I will not discard it.