I'm not sure if you're kidding, but the US dollar is not a ‘global currency’ in the sense that it is the only currency that is legal tender and that is regulated from a central (global) bank. The global socialists have been trying to destroy the US economy and the US dollar for decades. To implement a new monetary unit that is issued and regulated from a UN-type of economic ministry would mean total control over the world's population (except for the survivalists who are entirely independent) and the end of all nations as sovereign nations.
In short, all peoples of all the world would be reduced to a global feudalism.