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.