Beijing mouthpieces like China Daily are working overtime to warn yuan bulls not to take this year’s rally too far. A case in point was a headline this week declaring that the “Rapid Rise of the Yuan Is Unsustainable.” Fair enough. But to what extent is the yuan surging toward 6 to the dollar really President Xi Jinping’s call? Academics like Sheng Songcheng, former head of statistics and analysis at the People’s Bank of China, appear deputized from on high to get the word out. Sheng and other surrogates are throwing cold water on a key theory why Xi might tolerate a rising yuan: inflation.