Billionaire David Einhorn thinks gold is well on its way to becoming the world's ultimate reserve asset. The Green Light Capital founder said he believed the metal had already begun to replace US Treasurys as the top reserve asset among the world's central banks, attesting to its safe-haven status and shakier confidence in the US macro and fiscal outlook. Einhorn pointed to reports that China has told its banks to scale back its holdings of US Treasurys . Meanwhile, central banks' appetite for