Aside from all this retaliation talk, I think the key focus is to develop COMAC into a mature line of airliners, C919, C929 and what not. That way you wouldn't have to impose sanctions on Boeing or Airbus. A strong and powerful COMAC would in fact mean Boeing and Airbus are OUT OF the Chinese market. Those two would be shut out of the Chinese market as its clear Chinese airlines would fly COMAC airliners to support Chinese industry. And having Boeing and Airbus completely out of China is going to change the game a big deal. You wouldn't even have to retaliate, just through *fair and proper* competition alone you could crush the previous Big Two.
For all the flak ARJ21 is getting, I think it's a beautiful plane, and despite the heavier load the noisy but powerful engines are a fit for serving the high altitude western China region. It may have been slow, but they got the right fit, and that's what matters.
I can't wait to fly a COMAC C939 from Nairobi to Lagos years from now. Big Three airline makers ABC, thank you.