What if China had been unified by Fu Jian's Qin state? The Battle of the Fei River seems like an obvious source of divergence, where a victory could have helped bring about the collapse of the Jin. The point itself, however, probably has to be beforehand in the planning and execution of the campaign which IOTL was very poor even given that some of the accounts of the Qin army's performance were Jin propaganda. I think that if Fu Jian had waited and invested more time into training his army, it could have conquered. Fu Jian seems to have possessed some quality of responsibility and character, and Wang Meng was a highly talented statesperson. It seems strange to me that Fu would suddenly do something so rash, ignoring warnings that the army was not ready, and it seems to me that this circumstance could have been prevented at a number of points.
What, then, if Emperor Xuanzhao had swept the Jin away? What would his China look like? His family was full of capable military and administrative minds and Wang Meng seems to have been seen as just and efficient even by his enemies. This seems like an interesting opportunity for the unification of China to stick at a much earlier period than the Sui, as Fu Jian's state seems rather more sustainable than many of the other would-be dynasties of the same time.