Perhaps if the Shun, instead of the Qing, had successfully followed up the Ming, and then decided to move the capital south to Nanjing to be further away from disruptive Manchu influences?
Or perhaps the Qing momentum runs out after awhile (Wu Sangui doesn't switch sides, perhaps) and while they take Beijing and hold it, they are unable to make headway against the Southern Ming? Nanjing becomes the capital for long enough that it pretty much stays that way into the modern era. Modernization and mass education come in, and the Standard Dialect is based on Nanjinghua instead of Beijinghua.