Because it is a different "currency" than the dollar and subject to free market forces, it is impossible to maintain a 1 to 1 correlation. It is then better to let the market determine the value and hope it goes to the moon. For merchants accepting the Steem dollar, they should charge steem dollars for their sales at the market value. This is fair trade and exchange for equal value. If the merchant decides to accept Yuan automatically the merchant takes into account the value of the Yuan. Anything else is tantamount to theft.