Both the Brexit effect and the speculative chaos you propose are very short term. The fluctuations do not correspond in any way to the performance of the state and economy backing these currencies. Therefore, I think that if it benefits CNY, then only for a short timespan. However, if the US really tightens the screws on international trade, it will suffer longterm and so will its currency.
(And yes, I find the prospect of closed markets, increased tariffs and the like dreadful. There is no reason for the US to do that. This is different from Brexit though, since the EU conditions free movement of people and huge bodies of law on the trade agreements. A post-Brexit Britain may have more free trade than ever before since it can do its own agreements with any country - like any sovereign nation should.)
I don't see British trade expanding post brexit, we will almost certainly loose a substantial portion of our financial services and over time car manufacturing, the only trade likely to increase is tourism.
(And yes, I find the prospect of closed markets, increased tariffs and the like dreadful. There is no reason for the US to do that. This is different from Brexit though, since the EU conditions free movement of people and huge bodies of law on the trade agreements. A post-Brexit Britain may have more free trade than ever before since it can do its own agreements with any country - like any sovereign nation should.)