Yea, about that... Remember FATCA (Foreign Account Tax Compliance Act)? Laws like FATCA (global reach) gave a legal precedent which authoritarian regimes will exploit once the genie is out of the bottle. https://twitter.com/melissakchan/status/1289248868677218305

Another thing to point out: any government can claim ETJ over any external territory they wish. For example, Netherlands could claim ETJ over Vanuatu if they seemed it necessary. But in order to claim to be effective in the external territory, claimant must be able to enforce it.

Usually enforcement is agreed either with the legal authority in the external territory, or with a legal authority that covers both territories. Regarding Hong Kong NSL, it remains to be seen whether or not any foreign government is actually willing to enforce the law. (Nope!)

The only problem arises when someone breaks NSL and they are, say, employee of a company which has a branch is China and/or Hong Kong. At this point, the law becomes a nasty affair.