But who will take over world reserve currency status?

World reserve currency was solved by Keynes and Joan Robinson in the 1940s. What you do is have a currency no country controls that acts purely for exchanging one national currency for another. Give it to the united nations or something.

If you take a national currency and make it a world reserve currency then the nation that does do has problems with balance of trade, deficits, and mathematically screws themselves over. This is because you currency becomes overvalued compared to those of over countries, meaning your domestic manufacturing has problems competing, among other things.

We already made the mistake of one national currency becoming the world currency post WW2. I hope its not a mistake the world chooses to repeat.

It will likely be a cryptocurrency or perhaps a basket of cryptocurrencies. You essentially want a way to store wealth directly on the Internet as it is the fastest and easiest way to reassign ownership of money or collateral. The nice benefit too, then is the U.S. (and no other country as well) is subject to the Triffin Dilemma.