Robert Samuelson says "No". I agree. If China were to do this, say to retaliate against US moves in the incipient trade war, they would take the risk of a huge capital loss and a weakening of the dollar that will make tariffs look like small potatoes. They would risk rising interest rate that will make the huge indebtedness of Chinese consumers and corporations even more unsustainable. And the US would easily find other purchasers for these treasuries, making the move self-defeating.
The other issue China faces is: if not treasuries, then what? China has a huge current account surplus. It means they are accumulating claims on the rest of the world. What should they buy? Euro-denominated assets? Foreign stock? Foreign real estate? Are any of these good options compared to treasuries? I can see drawbacks for each of them.
UPDATE: Michael Pettis elaborates.