I agree with Hats' post above. [Edit: Just read Hats' original post and it is excellent! Most of what follows here is a sloppier version of that]
I think that more than having a hyper specific project in mind, a SOP should try to demonstrate how you can formulate questions of anthropological interest and why the program you are applying to will help you develop those questions into a project that will produce new knowledge. Based on what you've said your broad interests are:
"(language/discourse as vehicles for power, social theory of objectivity and knowledge production, China, social media, science and environmental studies, technology and politics), "
You've got a region identified: China. You've also got some theoretical areas identified: Language and Power; Politics of Knowledge, Social Media, STS, and Environmental Anthropology. For your SOP try to identify what intersections of these areas you want to explore more and why. That could be specific enough of a project pitch at this stage so long as it is well articulated and matches up with interests at the universities you are applying to. Maybe its something about how language and social media platforms are involved in disseminating and producing knowledge about climate change in China. I have no idea and am making something up based on..well, nothing... but I think that is the type of leap you want to make. You want to situate yourself as having the potential to do something new and interesting while also showing connections to existing areas of scholarship that the department is already working on.
The faculty know you're project will likely change. They want to see how you think.
I don't know if this helps.