It will not be China as it doesn't have a floating currency. That is one of the prerequisites for becoming a reserve currency, that and removing capital controls.
Finally there has to be a certain willingness from other countries to accept this new currency and I just don't see the EU countries conducting all their international trade in yuan anytime soon.
Finally replacing the USD is just one part. The second part is how to stop the next currency from being weaponized just like the USD is/was. Without the answer to that question, then switching to a new reserve currency is just replacing one problem with another.