I remember it was discussed on the HK forum and today saw that the information on the HKIA website has been updated:
Courtesy Channel
Courtesy Channel service provides dedicated access and a security screening channel in the departure halls at Terminal 1 and Terminal 2 to facilitate passengers with special needs and passengers invited by airlines.
Passengers invited by the airline according to the airline's operation guidelines, please contact your airline concerned for the eligibility to use the Courtesy Channel service
HX now also lists courtesy channel as a benefit for their Platinum/ Gold members. Is there any info on eligibility (if at all), for the MPC members/ CX Premium Cabin pax? I wish I checked with the Avseco staff yesterday.