I haven't had a chance to check this out yet, but I was always partial to a second civ representing the Manchus/Qing Dynasty (as in 1SDANI's old modmodmod) rather than separate South/North China.
Actually, (North, aka the one China in 1.18) China has a "Qing Period", which changes its settler/war map, and it does adopt the "Qing" name, so that's already the case somewhat. The South China civ represents the southern dynasties, often in periods where the south was ruled by Han Chinese and the north was ruled by one of the various "barbarians", depending on the time period.
The usual timeline of events in the test games I run are as such:
Disunited China.
Qin unification period.
Han China.
3 Kingdoms --> NChina becomes Wei, SChina spawns as Wu
Either China gets reunified by one or the other faction, or one or both collapse from barbarians / stability.
NChina, if dead, usually respawns in the late 500s to 700s, and reunifies China.
NChina falls prey to either barbarians, instability or the Mongols.
SChina often respawns somewhere in this period, acts as Southern Song.
Mongols either wipe out both civs or fail to unify China, leaving Southern Song alive.
Mongols collapse; either SChina reunifies China or NChina respawns.
If NChina is not yet alive, it comes back during the Manchu period to reunify China, or at least secure most of the north.
Qing period, then it goes into the Taiping / Republic of China period, which admittedly I haven't tested much (I have been working on game balance up to the Dutch spawn).