I do understand the difference between bad things happening someplace and an American duty to intervene in that place. We do have a military duty to help get our own American citizens out, but once that's done, South Sudan is probably going to be on its own.
I hate to say it, but the Chinese are probably the best hope the Christian population of South Sudan has right now.
China wants oil, it needs stability in both Sudan and South Sudan to get the local oil, and for China's own reasons (i.e, the Uighurs), China is very concerned about radical Islam and would prefer to see their oil coming from people who have an economic interest in selling oil rather than seeing a tribal and religious war disrupt those oil supplies.
In other words, China does have a direct economic interest and may force a settlement.
But China is not known for respecting any sort of standard of human rights or constitutional government in imposing that settlement. Orderly government and economic progress, not freedom, is what motivates China.
Perhaps the best-case scenario under a forced Chinese settlement would be the Chinese installing some sort of business-oriented technocrat from the black Christian population of South Sudan and giving him the military muscle necessary to run an authoritarian government — and there are a lot worse possibilities for a Chinese-enforced settlement than that.
You make an excellent point about China and how its economic needs direct its foreign policy. It would be a major extension of their power to involve themselves in Africa to the extent you are describing. However their needs are huge and they are building a great navy to project power. Sub Sahara Africa is evolving with a militant Islamic population in much of the North and a largely Christian population in the South. As you point out the resource rich central area where they clash will be contested and the scene of continual bloodshed. If the Chinese establish a harsh peace, it would benefit the less aggressive Christians.
The role of China in Iran is also overlooked.China views Iran as a natural source of energy. It also views its seventy million citizens as a potential huge customer base for its export driven economy. It has absolutely no fear of a nuclear armed Iran, and knows the mullahs are not so foolish as to support China’s radical Muslims. Most importantly China bitterly abhors American political, military and economic intrusions in Asia. It bitterly resents the American imposed sanctions. Americans do not realize how Asians deeply resent foreigners ( read that white Europeans) involving themselves in Asia. The rational for WWII for the Japanese common citizen and most intellectuals was that Asia was humiliated by the British, French, Dutch and Americans not only economically dominating but directly ruling. Japan of course saw itself as Asia’s dominant and natural leader. China now views itself as such. Its inherent anti-American postures and actions in Asia should be viewed in that context.