Cathay is the launch customer and they don't arrive until at least 2021.
You probably know more than me about it. I read that the first flight of the -9X is planned for 2018 so, I assumed that deliveries to airlines would begin in 2019.
Also, the smart launch customers do not take the first aircraft off the production line as they are usually overweight and suffer from technical issues that are not experienced with aircraft that come from a "mature" production line (eg SQ are replacing their first five A380's because of this).
In recent times, new aircraft types have had a number of "launch customers" so CX is probably "a" launch customer - not "the" launch customer.
PS. I just checked the Boeing website and it states that the launch customers are Emirates, Etihad, Lufthansa and Qatar - no mention of CX.