For most people in the China-sphere, the US only brings death and destruction by abusing certain abstract concepts such as human rights, democracy, or through outright lies such as "Saddam's WMDs."
On this respect, let alone China being a US conduit to "rein in Iran," China's conceptualization of the US policy is the very anti-thesis of all that the US regime represents in the global arena.
China does business. It has no interest in the domestic affairs of a sovereign nation. Sovereignty is the highest virtue in the era of nation state and there is no going back on this.
We are confident that the solution to the historical challenges that Iran may be facing will come from the Iranian people, and the Iranian people only.
There has not been an instance in history that foreign intervention could be benign and result in a good way. One either looses the ability to make sovereign decision, or tumbles into terrorism and fascism.
To be sure, China will never dictate any ideology on a sovereign nation with a distinct culture and history. It is the US business as they seem to be so eager for it.
I would advise not to anticipate anything good from the US or others on any issues, including political rights. US will support dictators at the cost of people if it is to their own interests.
This is what Turkish progressives and liberals are learning to their own demise as the fascist-turning one-man rule is having all the privileges and respects from the US and the most EU.
Chileans and Argentinians have learned this the hard way, as well.
Change and progress lie in you and in your own historical dynamics. Have faith in them.