If China somehow manages to overtake USA (tbh I don't see it happening), the next major reserve currency will be the CNY*. Whether it would be gold backed or not, I don't know. Probably not.
If we're talking in the context of contemporary monetary policy, the CNY has no chance. With their export-based growth model and history of consistently devaluing the Yuan, it's just not attractive to hold. It's one of the reasons Chinese wealth is characterized by constant capital flight outside the country.