I've got no sense for China. I'm still waiting to find out more about how China will receive an actual console. It could be almost nothing, or it could be a huge ton. My biggest skepticism about China has to do with supply though. Nintendo is about to have trouble supplying the places where it is well established. I am not sure how they can supply China at the same time. It might just make Nintendo even more short supplied.
In the end, I still think Switch total sales will surpass PS2 even before China is taken into account. After adding in China who knows? It might be a drop in the bucket or it might double their total sales. I need to see how Nintendo is received there before I can decide.