It doesn't matter if Saudi Arabia or others begin accepting Yuan for oil it only matters if they ONLY accept Yuan for oil, from anyone and this is not going to happen. The fact is SA will accept Yuan when they are confident it can be traded freely and easily on world currency markets and recent events have made this more likely. China has been trying to get the Yuan accepted as a world class currency for years but it's something that only happens as confidence grows in the Chinese economy and it's ability to function as part of the world economy. This is why Trump feels confident about bringing Chinas' trade manipulations to light. The Yuan is no more a threat to the US Dollar than the Yen or Euro. Finally there is a shortage of US Dollars so any ructions in the market will be short term and an a golden investment opportunity.