If China want to dump its US holding fast, it could crash the dollars and China could lose a lot of its wealth, and if China use the dollars to purchase stuffs from around the world, like oil etc, that will perpetuate the dollar dominance. Any attempt to de-dollarize must be done gradually. Trading with the rest of the world in yuan is a good start. Since I don't think forcing the US to pay the import in yuan is possible, at least at this stage, diversifying export market from the US is also necessary to reduce the "import" of dollar. Of course, China also need to let the capital market open freely if it want the foreigners to use yuan.