I think he's asking if there's been any sort of demand from the HK government to the various ISPs to start implementing such a thing, which I'm unaware of. Looks like the HK ISP association is getting out in front of the entire idea and issuing a clear statement.

Anyone that's been watching HK for the past 20 years would find it obvious that the PRC government intends to slowly integrate it into mainland China, and absorb it into the same legal framework, slowly but surely. Eventual end state goal would be laws indistinguishable from across the "border" in Shenzhen.

Sure, the threat of using "Emergency Regulations Ordinance" seems credible. Though that makes one ask of all the hypothetical outcomes which according to https://www.elegislation.gov.hk/hk/cap241 includes "arrest, detention, exclusion and deportation;", "authorizing the entry and search of premises;" etc, why is selective internet blocking the one that gets a pre-emptive denouncement rather than say randomly getting snatched at home by the police?