Im planning to book a tickect on ex-China Flight to HND (2019's September). I called CX's hotline to see if I can do a waitlist for the flight.

After giving time information, they said since my flight for China-HKG doesn't have seat right now(Seems blocked).
They said: "Waitlist doesn't in revenue tickect because we cannot guarantee if there's seat for you."

My Question is: Does CX provide waitlist for revenue ticket? Only in full fare class?