The world reserve currency is the US dollar. Even if a central bank holds gold as a store of value, they price it and their own currency in the US dollar. If any commodity was to be labeled a de-facto 'world currency' it would be petroleum, as it is a commodity that everyone MUST purchase in some fashion.
The monetary supply of the US dollar is determined by the Fed, which has no oversight from or obligation to the countries which that monetary supply affects. It's clear moral hazard, on a global scale.
people would still use fractional reserve lending, and credit. But, no one sovereignty would be in control of the supply of the the medium of exchange they used.
I'm not arguing it would improve anything, but it would certainly be different.