I've seen some speculation here on the boards that if the Roman Empire had survived or reformed after the Fall that we could end up with a China-like situation in Europe; sometimes dissolving, but always coming back together, with relatively homogeneous culture and language.
However, I've never seen it looked at the other way around: WI China had never had a stable Imperial system, and instead remained permanently divided into many competing kingdoms and states, like Europe or India? There might be some attempts at uniting all the Chinas, but, like the Romans, Guptas, or Mauryans, they would never work out in the long run. My guess at the best POD is to have a much longer Warring States period--in fact, to never have that period collapse, but just keep going on and on and on. Qin Shi Huangdi never gets it together to conquer everyone, and no Empire is ever founded.