It would be used in addition to copper. Circuit boards are currently made out of copper for various reasons, I don't think you would use gold for PCB traces eve

It would be used in addition to copper. Circuit boards are currently made out of copper for various reasons, I don't think you would use gold for PCB traces even if the materials were cheap. With copper you can use ferric chloride and simple photoresist to etch the board, with gold you would need something more powerful like aqua regia. Gold also has some undesirable properties like the various awful gold-aluminum intermetallics that it can form, and it suffers from poor solderability. I think more likely we would see ENIG as a standard / default plating instead of HASL. Traces would continue to be made out of copper or aluminum depending on what you are optimizing for, plated with gold (over a layer of zinc or nickel) to protect them from corrosion, and with various tin/nickel/etc pads for solderability.